Francis Darwin

“ Hales says in relation to greenhouses, "it is certainly of as great importance to the life of the plants to discharge that infected rancid air by the admission of fresh, as it is to defend them from the extream cold of the outward air." ”

“ It may be fairer to follow Sachs in linking these great men together and to insist on the wonderful fact that before Malpighi's book in 1671, vegetable physiology was still where Aristotle left it, whereas 56 years later in 1727 we find in Hales' book an experimental science in the modern sense. ”

“ He continues in the following delightful passage: "And could our eyes attain to a sight of the admirable texture of the parts on which the specific differences in plants depends [sic] what an amazing and beautiful scene of inimitable embroidery should we behold? what a variety of masterly strokes of machinery? what evident marks of consummate wisdom should we be entertained with?" To conclude what has been said on Hales' chronological position—Ingenhousz, the chief founder of the modern point of view on plant nutrition, was born 1730 and published his book On Vegetables, etc. ”

“ An error corrected—Hales' scientific contemporaries—Physiology or Physics—Hales the Founder of the experimental method in Physiology—His style—Cambridge days—Teddington—Vegetable Staticks—Experiments described—Transpiration—Root Pressure—Assimilation—Practical application to greenhouses—Distribution of growth first measured—Hales' other activities—Sachs' tribute.
In attempting to give a picture of any man's life and work it is well to follow the rule of the Dictionary of National Biography, and begin with the dates of his birth and death. ”

“ The authorities for the life of Hales are given in my article on him in the Dictionary of National Biography. Botanists in general probably take their knowledge of the main facts of his life from Sachs' History of Botany. It is therefore worth while to point out that both the original and the English translation (1890) contain the incorrect statement that Hales was educated at Christ's College, Cambridge, and that he held the living of Riddington, whereas he is one of the glories of Corpus, and was perpetual curate of Teddington. ”

“ Whewell points out in his History of the Inductive Sciences [4] that the Physiologist asks questions of Nature in a sense differing from that of the Physicist. The Why? of the Physicist meant Through what causes? that of the Physiologist—To what end? This distinction no longer holds good, and if it is to be applied to Hales it is a test which shows him to be a physicist. For, as Sachs shows, though Hales was necessarily a teleologist in the theological sense, he always asked for purely mechanical explanations. ”

“ Hales (p. 143) was one of the first [28] to make the well-known experiment—the removal of a ring of bark, with the result that the edge of bark nearest the base of the branch swells and thickens in a characteristic manner. He points out that if a number of rings are made one above the other, the swelling is seen at the lower edge of each isolated piece of bark, and therefore (p. 143) the swelling must be attributed "to some other cause than the stoppage of the sap in its return downwards," because the first gap in the bark should be sufficient to check the whole of the flowing sap [29] . ”

“ Thorpe points out the magnitude of the discovery that Priestley missed, and it may be said that Hales too was on the track and had he known as much as Priestley it would not have been phlogiston that kept him from becoming a Cavendish or Lavoisier. What chiefly concerns us however is the bearing of Hales' chemical work on his theories of nutrition. He concludes that "air makes a very considerable part of the substance of Vegetables," and goes on to say (p. 211) that "many of these particles of air" are "in a fixt state strongly adhering to and wrought into the substance of plants [33] . ”

“ Hales' belief that plants draw part of their food from the air, and again that air is the breath of life, of vegetables as well as of animals (p. 148) , are based upon a series of chemical experiments performed by himself. ”

“ As regards the action of light on plants, he suggests (p. 327) that "by freely entering the expanded surfaces of leaves and flowers" light may "contribute much to the ennobling principles of vegetation." He goes on to quote Newton (Opticks, query 30) : "The change of bodies into light, and of light into bodies is very conformable to the course of nature, which seems delighted with transformations." It is a problem for the antiquary to determine whether or no Swift took from Newton the idea of bottling and recapturing sunshine as practised by the philosopher of Lagado. ”

“ The later discoverers in chemistry are of the following dates, Black 1728—1799, Cavendish 1731—1810, Priestley 1733—1804, Scheele 1742—1786, Lavoisier 1743, guillotined 1794. These were all born about the time of Hales' zenith, nor did he live [3] to see the great results they accomplished. But it should not be forgotten that Hales' chemical work made more easy the triumphant road they trod. ”

“ This idea of ventilating greenhouses he carried out in a plant house designed by him for the Dowager Princess of Wales, in which warm fresh air was admitted. The house in question was built in 1761 in the Princess's garden at Kew, which afterwards became what we now know as Kew Gardens. ”

“ In this—a tentative experiment—he made the mistake of not re-measuring his plants at short intervals of time, but it was an admirable beginning and the direct ancestor of Sachs' [38] great research on the subject.
In his discussion on growth it is interesting to find the idea of turgescence supplying the motive force for extension. This conception he takes from Borelli [39] .
Hales sees in the nodes of plants "plinths or abutments for the dilating pith to exert its force on" (p. 335) ”