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, and the influence of 

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

 lating cells. Starch ' {amylvin) 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 l)e the first chemical prod- 

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

 of oxygen liljerated approximately equal to that of CO^ taken in, 

 is in harmony with the assumption that a carbohydrate is the 

 product of "^assimilation : 12C0, + lOH^ = 240 -j- C„HJJ,„ . 

 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, and H^O first unite to form an aldehyde 

 (alcohol), and this is polymerized into a carbohydrate (CO, + 

 H,0 = Oj + CH„0). LoEW produced a sugar (CeH,,Oe) out of 

 the aldehyde formed from formic acid and limewater. 



Under favorable circumstances starch-formation maj' 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^. Among many 

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

 of the leaf and other tissues during the night.'' 



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 



' As a note ou 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 macroscopically by a blue or dark-blue coloration of the starch-grains. 



^ For particulars see the works of Sachs. 



