18 STliUCTURJb: AND PlIYSIOLOCiY OF SEED PLANTS 



C. Describe the color and texture of the outer coating of 

 the seed. With a scalpel or a very sharp knife cut across 

 near the middle a seed that has been soaked in water for 

 twenty-four hours. Examine with the dissecting microscope 

 and sketch the section thus treated. 



D. Taking another soaked seed, chip away the white outer 

 shell, called the testa, and observe the thin, greenish, inner 

 skin with which the kernel of the seed is closely covered. 



E. Strip this off and sketch the uncovered kernel or embryo. 

 Note that at one end it tapers to a point. This pointed 

 portion, known as the hyioocotijl, after the seed sprouts will 

 develop into the stem of the plantlet. Split the " halves " of 

 the kernel, seed leaves or cotyledons, entirely apart from each 

 other, and note where and to what extent they are connected. 



F. 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° Fahrenheit (21° Centi- 

 grade) 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 plmnule or first bud. 



6. Examination of the bean. Study the seed, both dry and 

 after twelve hours' soaking, in the same way in which the squash 

 seed has just been examined. 



A. Notice the presence of a distinct plumule, consisting of a 

 pair of rudimentary leaves with a minute stem, between the 

 cotyledons, just where they are joined to the top of the 

 hypocotyl. In many seeds (as the pea) the plumule does 

 not show the distinct leaves, but in all cases it contains the 

 growing point, the tip of the stem from which all the upward 

 growth of the plant is to proceed. 



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

 the cotyledons, after the bean has been split open. 



Note the cavity in each cotyledon caused by the pressure of 

 the plumule and of the hypocotyl. 



