STRUCTURE AND GERMINATION OF SEEDS 23 



portion, and compare the two. Repeat this experiment 

 with the Pea. We thus see that the cotyledons of the 

 Bean and Pea contain much starch, and it is chiefly this 

 which gives them their value as food. 



The seeds of the Bean and Pea agree closely in their 

 general structure, e. g. they consist merely of a skin and 

 an embryo. Many seeds, however, are more complex, 

 while some so-called ' seeds ' are really fruits, e. g. those 

 of the Sunflower (Fig. 8, 1). Here we find a triangular 

 fruit with a narrower end, which was attached to the 

 receptacle, and also a broader end on which is a scar (sc), 

 left when the corolla and style dropped off. The outer 

 ribbed fruit-coat (2 pe) is hard and brittle, and on removing 

 it a single seed will be found covered by a thin testa (2 t) . 

 Such a dry, hard, one-seeded fruit is called an achene or 

 nutlet. Look for the short stalk (fu) which attaches the 

 seed to the pointed end of the fruit. Remove the seed- 

 coat and examine the embryo, noting the radicle (ra) at 

 the pointed end and the two flat cotyledons (c), between 

 which is the small plumule (pi). Test the cotyledons 

 with iodine solution : do they contain starch ? If a thin 

 section, treated with iodine solution, is examined under the 

 microscope, the cells will be seen to contain a number of 

 small yellowish granules. These are protein or nitro- 

 genous bodies called aleurone grains (similar granules may 

 also be found in the Bean, Pea, and Potato) ; there will 

 also be seen many bright globules which do not stain with 

 the iodine solution. If, however, a section is placed for 

 a while in ether the globules dissolve ; also, if a drop of 

 1 per cent, solution of osmic acid is placed on another 

 section, the globules stain a blackish brown. These tests 

 prove that the cotyledons contain protein or aleurone 

 grains and much fatty oil. Oil is a common storage 

 material in seeds, and often replaces starch. 



Endosperm. Food stored outside the embryo. The Ash 



