104 



PHYSIOLOGY. 



of germination of seeds common among monocotyledonous plants. 

 If the seeds are covered with sand, and 

 kept in a moist place, they will germi- 

 nate readily. 



213. How the embryo backs out of 

 the seed. The embryo lies within the 

 mass of the endosperm; the root end, 

 near the smaller end of the 

 seed. The club-shaped 

 cotyledon lies near the 



Fig. 94. 



Germination of castor-oil bean. 



middle of the seed, surrounded firmly on all sides by the endo- 

 sperm. The stalk, or petiole, of the cotyledon, like the lower 

 part of the petiole of the leaves, is a hollow cylinder, and 

 contains the younger leaves, and the growing end of the stem 

 or bud. When germination begins, the stalk, or petiole, of the 

 cotyledon elongates. This pushes the root end of the embryo 

 out at the small end of the seed. The free end of the embryo 

 now enlarges somewhat, as seen in the figures, and becomes the 

 bulb, or corm, of the young plant. At first no roots are visible, 

 but in a short time one, two, or more roots appear on the enlarged 

 end. 



214. Section of an embryo. If we make a longisection of 

 the embryo and seed at this time we can see how the club- 

 shaped cotyledon is closely surrounded by the endosperm. 

 Through the cotyledon, then, the nourishment from the endo- 

 sperm is readily passed over to the growing embryo. In the 

 hollow part of the petiole near the bulb can be seen the first 

 leaf. 



