210 HISTORY OF BOTANY 



He found the curve of intensity of exhalation fell rapidly 

 towards line A and also, but less steeply, towards E, and 

 then slowly to H. He thus denied that there was a second 

 maximum in the more refrangible part of the spectrum, 

 the existence of which had been asserted by Engelmann. 



Baeyer's hypothesis of 1870 led in the succeeding 

 years to various experiments in feeding green plants on 

 formaldehyde, the most successful of which were those 

 of Bokorny, who claimed to have obtained a gain in 

 weight in the green Alga, Spirogyra, after supplying it 

 with various substances which yielded formaldehyde 

 on decomposition. The chief argument used by Bokorny 

 and others was that formaldehyde was not poisonous 

 if supphed in minute quantities and under conditions 

 when it could be at once polymerised and so rendered 

 innocuous. 



In 1893 a paper by Brown and Morris appeared 

 which created quite a sensation in laboratories of plant 

 physiology, and to which I must make a brief reference. 

 The authors, while engaged on the determination of dia- 

 static enzymes in leaves, came to the conclusion (as did 

 also Gautier at an earlier date) that cane-sugar was 

 the first carbohydrate formed in photosynthesis, and, 

 further, that the larger part of the products formed in 

 the synthetic process never assumed the form of starch. 



You will remember that Boussingault, in the year 

 1868, concluded that the pathway of gaseous exchange 

 was not by the stomata but by the cuticle of the leaf, 

 and that Barthelemy supported him in this view. In 

 1894 F. F. Blackman, by aid of an ingenious piece of 

 apparatus, re-investigated the whole question. His ex- 

 periments led him to the conclusion that, under normal 

 conditions, practically all the carbon dioxide passed 

 through the stomata, both inwards and outwards, although 

 when the stomata were blocked and the tension of the 

 gas was sufficiently high, which it rarely was in nature, 

 some might pass through the cuticle. He pointed out 



