ASSIMILATION 81 



Nevertheless Hales is not quite consistent about the action 

 of light; thus (p. 351) he speaks of the dull light in a closely 

 planted wood as checking the perspiration of the lower branches 

 so that " drawing little nourishment, they perish." This is doubt- 

 less one effect of bad illumination under the above-named 

 conditions, but the check to photosynthesis is a more serious 

 result. In his final remarks on vegetation (p. 375) 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." 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. The site of Hales' greenhouse, which was only pulled 

 down in 1861, is marked by a big Wistaria which formerly 

 grew on the greenhouse wall. It should be recorded that 

 Sir W. Thiselton-Dyer 1 planned a similar arrangement inde- 

 pendently of Hales, and found it produced a marked improve- 

 ment of the well-being of the plants. 



It is an illuminating fact that though Hales must have 

 known Malpighi's theory of the function of leaves (which 

 was broadly speaking the same as his own), he does not as 

 far as I know refer to it. In his preface, p. ii, he regrets that 

 Malpighi and Grew, whose anatomical knowledge he appre- 

 ciated, had not " fortuned to have fallen into this statical* way 

 of inquiry." I believe he means an inquiry of an experimental 

 nature, and I think it was because Malpighi's theory was 

 dependent on analogy rather than on ascertained facts, that 

 it influenced Hales so little. 



There is another part of physiology on which Hales threw 

 light. He was the first I believe to investigate the distribution 



1 The above account of Hales' connexion with the Royal Gardens at Kew is from 

 the Kew Bulletin, 1891, p. -289. 



2 I am indebted to Sir E. Thorpe for a definition of statical. "Statical (Med.) 

 noting the physical phenomena presented by organised bodies in contradiction to 

 the organic or vital." (Worcester's Dictionary, 1889.) 



O. B. 6 



