4 Plant Morphology. 



Between it and the cotyledons is a chalky, less-coherent layer, — 

 the inner-seed-coat or tegumen. 



The Seedling of the Common Bean, 



Select a seedling which has its first pair of leaves well-devel- 

 oped. 



The seed-coats have been either partially or wholly thrown off. 



The hypocotyl has lengthened. The tap root arises from its 

 lower end. In the common Bean there are no roots arising from 

 any part of the stem except the lov/er end of the hypocotyl. In 

 the seedling of Indian Corn (Zea Mays) secondary roots occur. 

 The roots of both plants are fibrous. 



The first internode is greatly lengthened. The growing points 

 of the embryo are at the lower tip of the hypocotyl and at the 

 plumule. Here cell division takes place most rapidly. The 

 growth of the other parts depends more upon the increase in size 

 of cells already formed than upon cell division itself. 



The first pair of leaves are simple, thus differing from the 

 leaves of the mature plant. Note the gradation of leaves from 

 the much modified cotyledons to the compound leaves of the ma- 

 ture plants. They have a blade, petiole, and stipules. The sti- 

 pules of the Common Bean are inconspicuous and also vary, the 

 first two pairs being very small and united, the later ones larger 

 and free. Are the stipules of the single leaf united with each 

 other? The stipules are much larger in the Pea. Both belong 

 to the same Natural Order (Leguminosae). All plants of this 

 order have leaves with stipules. This is said to be a character of 

 the order. 



The terminal bud is the continuation of the plumule. 



Sketch one-half of the seed (f ) indicating the parts noted. 



Sketch a seedling (f ) at two or more stages of development. 



II. CASTOR OIL BEAN {Ricinus commanis L.). 



Upon the hilum is a wart-shaped appendage called a caruncle. 



With this as head and the rest as body, this seed was thought 

 by the ancients to resemble a "tick," a parasitic insect living 

 upon sheep, hence the generic name " Ricinus " meaning a Tick. 



The brittle outer-seed-coat is sculptured on the outside, a char- 



