148 



APPLIED BIOLOGY 



kept moist. Notice a peculiar hump (the peg) which develops on 

 the hypocotyl and when that grows longer the seed-coats are pried 

 open. Notice how the stem part of the hypocotyl is looped as it 

 comes from the seed-coat. In specimens planted in the ground this 

 loop is the first part to appear, soon dragging the cotyledons out 

 after it, and then the looped stem straightens out and lifts up the 

 two green cotyledons. 



Compare cotyledons of squash and bean seedlings at various stages 

 until the second pair of leaves develop, and write a brief account. 



Take a squash seed that has sprouted, and open as before. Be- 

 tween the cotyledons, and fastened to the upper end of the hypocotyl, 

 is the epicotyl, which is too small to be easily seen in a dry seed 

 and one must look for it after it has grown larger. Examine the 

 epicotyl in seedlings of various sizes. 



Compare a squash seed with a bean seed in the following points : 

 texture of seed-coat, number and thickness of cotyledons, 

 the more leaf-like cotyledons, and relative size of epicotyl. Record 

 these facts in tabular form. 



. 138. Seed of Castor-Oil Plant. (L) Materials : dry seeds 

 (poisonous). Seeds soaked in water for at least 24 hours. A series 



of sprouted specimens to show the de- 

 velopment of the seedling up to the 

 time the epicotyl is well developed. 



Examine dry castor-oil seeds and 

 note color and markings. The meaning 

 or use of these is not known. In fact, 

 it is not necessary to assume that they 

 have a use ; for hundreds of beautiful 

 minerals are buried, and therefore their 

 color as seen in the light cannot be of 

 use. Some authors have imagined that 

 castor-oil seeds resemble beetles or ticks 

 so closely that they would be avoided 

 by birds, but there is no scientific evidence to support this theory. 

 Examine a castor-oil seed which has been soaked in water. The 

 point of attachment in the ovary (that is, the hilum) and the mi- 

 cropyle are near the rounded projection at the small end of the seed. 

 Crack the shell-like seed-coat, and carefully remove it. The "ker- 

 nel" thus exposed is covered with a delicate membrane (inner seed- 

 coat). Carefully remove this. The double "kernel" will at first 

 be taken to correspond to the embryo of a bean with very thick 

 cotyledons; but by carefully separating the two halves of water- 



FIG. 42. Castor-oil seed, c, hy- 

 pocotyl; st, cotyledon; e, en- 

 dosperm. (From Osterhout.) 



