THE SEED AND ITS GERMINATION 



noticing that they are only attached for a very little way next to 

 the hypocotyl, and observe the thickness of the halves and the slight 

 unevenness of the inner surfaces. These halves are called seed-leaves 

 or cotyledons. 



Have ready some seeds which have been soaked for twenty-four 

 hours and then left in a loosely covered jar on damp blotting paper 

 at a temperature of 70 or over 

 until they have begun to sprout. 



Split one of these seeds apart, 

 separating the cotyledons, and 

 observe, at the junction of these, 

 two very slender pointed objects, 

 the rudimentary leaves of the 

 plumule or first bud (Fig. 1, p). 



3. Examination of the Bean*. 

 Study the seed, both dry and 

 after twelve hours' soaking, in 

 the same general way in which 

 the squash seed has just been 

 examined. 1 



Notice the presence of a dis- 

 tinct plumule, consisting of a pair 

 of rudimentary leaves between 

 the cotyledons, just where they 

 are joined to the top of the hypo- 

 cotyl. In many seeds (as the pea) 

 the plumule does not show dis- 

 tinct leaves. But in all cases 

 the plumule contains the growing 

 point, the tip of the stem from 

 which all the upward growth of 

 the plant is to proceed. 



Make a sketch of these leaves as they lie in place on one of the 

 cotyledons, after the bean has been split open. 



1 The larger the variety of bean chosen, the easier it will be to see and 

 sketch the several parts. The large red kidney bean, the horticultural bean, 

 or the lima bean will do well for this examination. 



FIG. 2. The Castor Bean and its 

 Germination. 



A, longitudinal section of ripe seed ; t, 

 testa ; co, cotyledon ; c, hypocotyl ; 

 B, sprouting seed covered with endo- 

 sperm ; (7, same, with half of endo- 

 sperm removed ; D, seedling ; r, pri- 

 mary root ; r', secondary roots ; c, arch 

 of hypocotyl. 



