TISSUES AND SIMPLE ORGANS. 131 



We shall now further discuss the process of assimilation. 



Each individual chlorophyll-grain may be designated as a work- 

 shop of assimilation. The chief requirements for this assimilation 

 in the chlorophyll are the presence of CO 2 and the influence of 

 diffuse or direct sunlight. Water is already present in the assimi-^ 

 lating cells. Starch ' (amyliim) in the form of starch-grains is, in 

 the majority of instances, the rapidly formed product of this 

 assimilation, though it is not the immediate chemical product. 

 Before solid starch-grains can be formed there must be a product 

 of assimilation, also a carbohydrate, which is soluble in water, as 

 some form of sugar ; even this may not be the first chemical prod- 

 uct. The experimental-physiological fact that there is a volume 

 of oxygen liberated approximately equal to that of CO 2 taken in, 

 is in harmony with the assumption that a carbohydrate is the 

 product of assimilation : 1 2CO 2 + 10H 2 O = 24-O + C W H 10 O 10 . 

 According to recent investigations (ARTHUR MEYER), the formation 

 of soluble carbohydrates (devoid of starch) predominates in the 

 chlorophyll of monocotyledons, while starch-formation predomi- 

 nates among dicotyledons. In regard to the immediate, still un- 

 known, product of assimilation we may state that, according to the 

 hypothesis of BAYER, CO 2 and H 2 O first unite to form an aldehyde 

 (alcohol), and this is polymerized into a carbohydrate (CO 2 -f- 

 H 2 O = O 2 + CH 2 O). LOEW produced a sugar (C 6 H 12 O 6 ) out of 

 the aldehyde formed from formic acid and limewater. 



U nder favorable circumstances starch-formation may take place 

 in a few minutes. The starch that is formed will disappear in 

 the dark, also in the light in the absence of CO 2 . Among many 

 plants the starch formed during the day is carried into the petiole 

 of the leaf and other tissues during the night. 2 



Chlorophyll-grains as the workshop of our most essential food- 

 substance, bread, deserve special attention. Our present scientific 

 knowledge does not enable us to furnish even an approximate 

 substitute should the above-described chlorophyll activity cease 

 altogether. Science does not even comprehend the chemical 



1 As a note on microcbemistry may be added. Iodine is only slightly soluble 

 in water, more so in solution of KI or alcohol. All these solutions, more particu- 

 larly the stronger, serve to demonstrate the presence of starch both microscopi- 

 cally and rnacroscopically by a blue or dark-blue coloration of the starch-grains. 



2 For particulars see the works of SACHS. 



