202 Plant Physiology 



upon light. Notice the color of seedlings which have 

 grown in the dark and of grass beneath a board or pile of 

 leaves. The epidermal cells of seed-plants are commonly 

 colorless, yet the guard cells of the stomata are important 

 exceptions. Nevertheless, there are certain structures 

 which, supplied with a good food-supply, contain chloro- 

 phyll, even when produced in the dark ; for example, the 

 cotyledons of pine. 



The white or yellow areas of variegated leaves may 

 contain no chlorophyll ; but leaves which are during 

 growth brown, red, or otherwise highly colored contain 

 chlorophyll bodies, the color in such cases being veiled by 

 the presence of other pigments often present in the cell- 

 sap. The diverse pigments of many algae exhibit a 

 greater complexity. In the great majority of plants the 

 chlorophyll bodies are discoidal or button-like forms (often 

 lenticular or more nearly plano-convex), although in cer- 

 tain of the algae (Spirogyra, desmids, etc.) they may 

 possess unusual peculiarities of shape. The intimate 

 structure of the chloroplast is none too well known. 

 Briefly, it may be said that there is a cytoplasmic stroma, 

 and within this is contained the green pigment, somewhat 

 diversely deposited in different cases. 



108. The nature and properties of chlorophyll. - - By 

 means of alcohol, chlorophyll may be extracted from plants, 

 leaving the tissues practically white. Either ethyl, 

 methyl, or denatured alcohol may be employed, and the 

 process is greatly facilitated by carefully bringing the 

 alcohol to a temperature close to its boiling point over a 

 water-bath. Seedling plants of the horsebean, small ce- 

 reals and grasses, radish, or nasturtium afford as favorable 



