194 R-J- Harvey Gibson. 
service. For this purpose nature has provided the leaf with 
numerous special glands or bellows for the sweating forth and 
gradual elimination of moisture, so that the sap, being thereby 
condensed, may the more readily be digested in the leaves.” 
It would seem therefore that Malpighi regarded leaves primarily 
as digestive not as manufacturing organs, and that he thought the 
digestion was a fermentative process; “the power of the sun’s 
rays,” as Sachs phrases it, is concerned in that process however 
only indirectly, viz., by raising the temperature of the surrounding 
air and so aiding in the evaporation of what was of no service. 
How Sachs could have read into Malpighi’s words a constructive 
effect of solar energy on the “ blended sap ” and at the same time 
denied to him any knowledge of stomata is incomprehensible. 
Hales’s contributions to Vegetable Physiology are contained 
in the first volume of his well-known “ Statical Essays ” and quite 
recently an interesting summary of his life and an analysis of his 
work has appeared from the pen of Sir Francis Darwin, published 
in Oliver’s Makers of British Botany (1913). Darwin writes, 
“ Hales, of course, knew nothing of stomata,” but on page 160 of 
the 1731 edition of the Essays we read:—“ I found little or no air 
came either from the branches or leaves except what air lay in the 
furrows and in the innumerable little pores of the leaves which are 
plainly visible with the microscope.” Hales also was quite familiar 
with Grew’s observations on stomata, for he quotes his statements 
on the subject. 
Darwin also says that Hales “does not in any way distinguish 
between respiration and assimilation,” an opinion scarcely supported 
by the following sentence:—“We may therefore reasonably conclude 
that one great use of leaves is what has long been suspected by 
many, viz., to perform in some measure the same office for the 
support of vegetable life that the lungs of animals do for the support 
of animal life; plants very probably drawing through their leaves 
some part of their nourishment from the air.” Crude as was the 
knowledge of animal physiology in the time of Hales it can scarcely 
be believed that Hales conceived the lungs to be nutritive organs, 
and the sentence quoted therefore seems rather to indicate that he 
regarded the leaves as serving both as a respiratory and as a 
nutritive apparatus. 
Up to the middle of the 18th century, however, it cannot be 
said that even the foundations of the modern theory of photo¬ 
synthesis had been laid; nor indeed, was that possible till the 
