158 TYPE STUDIES 



prominent nucleus ; (c) frequently the presence of a single canal 

 cell (ventral canal cell) above the egg ; (d) a layer of cells differen- 

 tiated from the endosperm, forming a jacket around the egg ; (e) one 

 or tvf o tiers of cells, four cells in a tier, above the egg, and repre- 

 senting the neck of the much-reduced archegonium (see Principles, 

 Fig. 300, D). 

 2. In the male gametophyte : should the tips of pollen tubes be found 

 entering the necks of archegonia they may be expected to show tvpo 

 large sperm nuclei, and possibly the remains of the tube nucleus, now 

 degenerating, with that of the stalk cell also. 



L. The seed. Take seeds from an open cone. It generally opens 

 at the end of the third summer, when the cone is approxi- 

 mately two years and three months old. Sketch to show the 

 wings. Section such seeds, or, better still, cut open. some of 

 the large edible seeds of the nut pines, pinon, obtainable 

 from fruit dealers. Note : 



1. The tough seed coat, or testa, which is the ripened integu- 

 ment, and beneath the testa a membranous seed coat which 

 is largely the remains of the nucellus. 



2. The endosperm, filling the seed except for the embryo. 

 The former is a development from the endosperm of the 

 embryo sac and consequently gametophytic in character. 



3. The straight embryo,' developed from a fertilized egg, 

 attached to the micropylar end of the seed by a stispensor 

 and imbedded in the endosperm. The embryo consists of 

 a short hypocotyl, bearing above a circle of cotyledons. 



Construct a diagram of a lengthwise section of a seed to 

 show these structures in relation to one another. 

 M. The germination of the seed. The pine seed germinates 

 rather slowly, but it will be of interest to plant some and 

 watch them as they sprout, comparing them with such seed- 

 lings of the angiosperms (squash, bean, pea, corn, etc.) as 

 may have been studied. 



Reference. Principles, Sees. 350-356. 



Questions. What are the growth habits of the pine ? What 

 are the peculiarities of its foliage ? its adaptation to drought 



