Hypothallus

“ The peridium may be double, varies in texture, color, persistence, and so forth, as will be more fully set forth in the several specific descriptions. The peridium blends with the hypothallus below when such structure is recognizable, either directly, when the sporangium is sessile, or by the intervention of a stipe. The stipe may be hollow, may contain coloring matter of some sort, or may even contain peculiar spore-like cells or spores; is often furrowed, and in some cases shows a disposition to unite or blend with the stalks of neighboring sporangia. ”

“ Fructification plasmodiocarpous, elongate, hamate, annulate or irregularly repent, very dark brown, rough, the peridium of two layers, the outer closely adhering, dark brown, thick, opaque, the inner delicate, membranous, very thin, transparent, iridescent, rugulose, rupturing irregularly; hypothallus none; spores in mass pale yellow with a greenish tinge, by transmitted light nearly colorless, large, globose, minutely spinulose, 12.5 μ. ”

“ A more minute species than Didymium serpula, without characteristic thickenings upon the threads of the capillitium, and wanting the peculiar large cells of this species.
II. SPUMARIA, Pers. Æthalium composed of numerous elongated, irregularly-branched sporangia, more or less closely compacted together and confluent, seated upon a well-developed common hypothallus; the walls of the sporangia [Pg 65] a thin membrane with an outer layer of minute, stellate crystals of lime. ”

“ Apart from the peculiar incrustation in the present species, the larger spores, and especially the peculiar white hypothallus, are distinctive. The method of dehiscence is also different. In P. corticalis the line of cleavage before spore dispersal is indicated by a definite band surrounding the sporangium. Nothing similar appears in the gray specimens of the present form, although the dehiscence is quite as certainly circumscissile. The habitat in American specimens is the [Pg 245] outer surface of the bark, which causes the species generally, by protective coloration, to be overlooked. ”

“ Æthalium pulvinate, 2–8 cm. broad, at first silvery white, later less lustrous, the cortex irregularly and slowly deciduous; hypothallus at first conspicuous as a white margin extending round the entire aethalium, evanescent without, but persisting as a firm membrane beneath the spore-mass, pseudo-capillitium abundant, tending to form erect central masses which persist long after the greater part of the fruit has been scattered by the winds; spore-mass umber, spores by transmitted light pale, reticulate over about two-thirds of the surface, the remainder slightly warted, 8–9 μ. ”

“ Sporangia, in typical forms, gregarious, globose or depressed-globose, gray or snow-white, stipitate; the peridium a thin iridescent membrane covered more or less richly with minute crystals of lime; the stipe when present, snow-white, fluted or channelled, stout, even; columella white, conspicuous; hypothallus usually small or obsolete; capillitium of delicate branching threads, usually colorless or pallid, sometimes with conspicuous calyciform thickenings; spores violaceous, minutely warted or spinulose, 8–10 μ. ”

“ Lister in Mycetozoa Pl. XL., c. draws the capillitium much more delicate than it appears in our specimens. The hypothallus is sometimes noticeable under some of the sporangia where closely crowded, but is not a constant feature.
Rostafinski (by typographical error?) confused in the Monograph, pp. 164, 165, this species with Persoon's Physarum confluens. In the Appendix he substitutes the Friesian nomenclature. Persoon's description of his species is insufficient, and throws no light on the problem whatever.
Rare. Iowa; Black Hills, South Dakota. Reported common in Europe. Canada ”

“ Thus it may simply form a flat, cake-like mass, aethalium, internally divided into an indefinite number of ill-defined spore cases, sporangia; or the plasmodium may take the form of a simple net, plasmodiocarp, whose cords stand out like swollen veins, whose meshes vary both in form and size; or more commonly the whole protoplasmic mass breaks up into little spheroidal heaps which may be sessile directly on the substratum, or may be lifted on tiny stems, stipitate, which may rest in turn upon a common sheet-like film, or more or less continuous net, spreading beneath them all, the hypothallus. ”

“ These ascending branches are in many cases, probably in all, real, though as yet imperfectly developed, columellæ. They rise, at least in many cases, directly from the hypothallus, each is central to an individual sporangium, rises to about two-thirds its height, but never attains the summit. The sporangia are so crowded that many are choked off below, never reach the top of the æthalium. In such cases the columella may cease at the sporangium-top. The columella bears cystiferous threads sparingly, if at all ”

“ They are not, however, true nucleated cells, and the body described as a nucleus is not such in reality. Nevertheless these large hyaline spheres do possess a special envelope, as I have recently convinced myself by the examination of ruptured central capsules of Thalassolampe maxima, Thalassopila cladococcus, and Physematium atlanticum (Pl. 1, figs. 2, 3) . The central capsule of these Collodaria becomes distended to most unusual dimensions (2 to 12 mm. in diameter) by the great development of these large hyaline vesicles, each of which measure from 0.1 to 0.5 mm. ”

“ The first generation proceeds directly from the spore, and consists of a simple green expansion which is short-lived and very small, not usually exceeding half the size of a small finger-nail. This prothallus, as it is termed, has small, root-like hairs which fix it to the earth or elsewhere. The prothallia are to be seen in large numbers on the sides of flower-pots in neglected greenhouses. Each little green scale is a young fern-plant during its sexual generation. The male and female organs are much the same shape as those of mosses. ”

“ Even if the hydathode is treated with sublimate solution, all the conditions for mechanical filtration still remain: the earth has moisture which can be taken up by the roots so that root-pressure still exists. The water is in all cases conveyed to the hydathodes through the vascular fibres, the cell walls of the hydathodes are still adapted for filtration, and yet they do not filter. Hence some other factor must join itself to the physico-mechanical process of filtration and affect or destroy it, and this factor can be found only in the protoplasm, the vital element of the cells ”

“ The sporangia are borne singly or in sori of two or three on the margin or under surface of leaves, the fertile pinnae of which differ more or less from the sterile segments. The sporangium is of considerable size, and dehisces by a median slit, the annulus being a more or less definitely limited horizontal ring of cells near the apex. The prothallus and sexual organs may resemble those of the Polypodiaceae; in Aneimia and Mohria the prothallus, though flattened, is not bilaterally symmetrical, the growing point being on one side; a filamentous type of prothallus is known in Schizaea. ”

“ The exogenous and endogenous hydatids may coexist in the same bearer. In the lower animals we commonly find the organs of the body occupied by numerous lobulated cysts, varying in size from a walnut to a goose’s egg, but sometimes rather larger. They are rarely solitary, being particularly liable to occupy both the liver and lungs in the same animal. The viscera are sometimes crowded with cysts. The hydatids do not usually protrude much beyond the surface of the infested organ, but lie imbedded within its parenchymatous substance. ”

“ In some cases the individual consists of a minute simple cell which multiplies by cell-division; in others the body or thallus is made up of a number of similar units, while in a great number of forms there is a well-marked physiological division of labour, as expressed both in the external division of the thallus into distinct organs corresponding in function to the root, stem, and leaves of the higher plants, and further in the high degree of histological differentiation of the tissues. In other thallophytes, again, the thallus is a coenocyte either unseptate or incompletely septate ”

“ No leaf-like appendages are borne on the thallus, but short glandular hairs occur behind the apex. The plant is composed throughout of very similar living cells, the more superficial ones containing numerous chlorophyll grains, while starch is stored in the internal cells of the midrib. The cells contain a number of oil-bodies the function of which is imperfectly understood. The growth of the thallus proceeds by the regular segmentation of a single apical cell. The sexual organs are borne on the upper surface, and both antheridia and archegonia occur on the same branch (fig. 3, A) . ”

“ Thallus foliose, but smaller and thinner than that of Peltigera, and devoid of trichomatic hyphae, more or less closely attached to the substratum by rhizoids; cortex well developed on both upper and lower sides; medulla well developed (Fig. 2) ; apothecia confined to the lower side of the thallus, marginal on narrow, slightly elongated lobes, thalloid margin persistent and crenate; hypothecium usually some shade of brown; hymenium [Pg 359] usually pale below and brown above; paraphyses simple or branched; spores brown, 4-celled, 8 in each ascus. ”

“ The hyphal filaments may be closely packed together and form a felted mass of compact tissue, which in cross section closely simulates the parenchyma of the higher plants. This pseudoparenchymatous form of thallus is particularly well illustrated by the so-called sclerotia; these are sharply defined and often tuberous masses of hyphal tissue covered by a firm rind and containing supplies of food in the inner hyphae. They are able to remain in a quiescent state for some time, and to resist unfavourable conditions until germination and the formation of a new individual take place. ”

“ Within the Lecideaceae, the line of evolution seems to have been in the direction of a well-developed exciple and from simpler to more complex spores. With the advance in these two directions has gone a slightly increased development of the thallus.
In structure, the thallus is crustose, and the thalli vary from inconspicuous, evanescent conditions to those which are conspicuous and sometimes even subsquamulous. Rarely the thallus extends upward as a veil which surrounds the apothecia laterally and suggests how the thalloid exciple of higher families probably arose. ”

“ In addition to the cell types described, it is a very common occurrence in these bulky forms for rhizoid-like branches of the cells to grow out, mostly from the cells at the periphery of the medulla, and grow down between the cells, strengthening the whole tissue, as in the Rhodophyceae. This process may result in a considerable thickening of the thallus. In many Laminariaceae the thallus also grows regularly in thickness by division of its surface layer, adding to the subjacent permanent tissue and thus forming a secondary meristem. ”

“ Thallus commonly granulose, and often passing into verrucose and chinky conditions, but scarcely ever areolate, sometimes scant and evanescent; apothecia usually minute or small, and commonly adnate, exciple weak and often becoming covered; hypothecium and hymenium passing from pale through shades of brown, the former becoming darker than the latter, this rarely tinged blue or violet above; spores hyaline, 2-celled. ”

“ On boiling with water the inner tissue swells up, the cell-walls being partly dissolved. Thin slices of the lichen are coloured reddish or pale blue by iodine water,—more distinctly blue, if previously treated with sulphuric acid. The colour spreads uniformly over the inner tissue, but no starch granules can be detected; the cortical layer is merely coloured brown by iodine. The white spots on the outer surface of the thallus are resolved by pressure under a plate of glass into minute round transparent granules, not coloured by iodine, and thick branched cells like those of the central layer. ”

“ It is possible that, in a given disease, a normal organ is not decomposed, although the same organ is readily attacked, if it has already undergone particular pathological changes. Thus it is quite possible that, for instance, a normal thyroid gland would not be decomposed by Basedow serum, while a gland originating from a morbus Basedowi would be subject to decomposition. Just as every case examined has to be thoroughly tested by clinical means, and its further course closely followed up, so also must the substrate to be employed be characterized exactly. ”

“ The other Thalassicollida differ from their common ancestral form, Actissa, mainly by the higher histological differentiation of the unicellular body. Whilst in Thalassicolla and Thalassolampe the nucleus remains a single sphere as in Actissa, it becomes branched or covered with radial blind saccules in Thalassopila and Thalassophysa; also the intracapsular protoplasm develops here a great variety of peculiar different corpuscles, as oil-globules, pigment-granules, concentric concretions, crystals, &c. ”

“ Now it seems possible that a circle between radicle and hypocotyl may be permeable to fluids, and thus have given rise to projections so as to expose larger surface. Could you test Welwitschia with permanganate of potassium: if, like my pegs, the lower surface would be coloured brown like radicle, and upper surface left white like hypocotyl. If such an idea as yours, of an absorbing organ, had ever crossed my mind, I would have tried many hypocotyls in weak citrate of ammonia, to see if it penetrated on line of junction more easily than elsewhere. ”