8 THE AMERICAN BOTANIST. 



cotyledous and yellow for the endosperm — it will serve to 

 bring out those structures more clearly. The colors suggested 

 are those that the plantlet usually wears in these parts or the 

 colors they usually assume when tested for foods. 



The foods stored in seeds may consist of starch, sugar, 

 oils, cellulose and proteids. The well-known iodine test is 

 best for starches. Pupils may scrape a few cells from the 

 cotyledon of the bean and by treating with iodine solution see 

 with the microscope the starch grains in the cells for them- 

 selves. Proteids will reveal themselves if treated with a drop 

 of nitric acid followed in a few minutes with a drop or two of 

 ammonia. They will also turn a rose, or dull red if moistened 

 with Millon's reagent and heated. The acid test is probably 

 as good as any. Oils will leave a permanent spot on clean 

 white paper when parts containing them are pressed upon it. 

 The seeds may also be ground up, the oils dissolved out with 

 ether or chloroform and obtained by evaporating the solvent. 

 Oils also turn black if treated with osmic acid, and red if 

 tested with an alcoholic solution of alkamin. Sugar and cellu- 

 lose in seeds may be disregarded. The reserve food in the 

 date is cellulose, but it is not essential that it be tested. Cel- 

 lulose turns blue if moistened with iodine solution and then 

 with strong sulphuric acid diluted with half its bulk of water. 



In investigating the question of what seeds need in order 

 to germinate, it does not seem worth while to perform experi- 

 ments to see if plants need warmth. Every pupil with enough 

 brains to understand botany knows that plants will not grow 

 in the cold. If it is desired to know at what temperature seeds 

 will germinate, it will need a long series of experiments be- 

 fore we can generalize, for seeds are not alike in these 

 requirements. Maple seeds are reported to be able to grow on 

 a cake of ice ; peas will grow with a very small increase in tem- 

 perature above the freezing point, but corn and tomato will 

 not. The fact that seeds need warmth is familiar to all. That 



