JUNIPER AND ARBOR VITiE 159 



arid cold ? Where is the resin and turpentine formed ? 

 Can you suggest any advantage to the plant in its produc- 

 tion ? How and when is pollen formed and how abundantly ? 

 How does it reach the ovule ? What is the history of the 

 carpellate cone after pollination ? When are the seeds 

 ripened ? What is the morphology of the pollen grain ? 

 Describe the male gametophyte, with its habits, after the 

 germination of the pollen grain in the pollen chamber. 

 Describe the structure of the ovule. Describe the female 

 gametophyte and its life habits within the nucellus (mega- 

 sporangium). Prom what does the embryo arise and how 

 does it obtain the food for its development? How many 

 generations are represented in the tissues of the seed? 

 Describe the life history, distinguishing between the sexual 

 phases, gametophytes, and the asexual phase, sporophyte. 

 Draw and arrange a series of diagrams illustrating the chief 

 stages throughout the life history, using two colored pencils 

 to designate the gametophytic and sporophytic generations 

 respectively (App. 18). Construct a life-history formula that 

 will express this succession (App. 18). 



139. The morphology of the juniper and arbor vitae. The juniper (JuniperMs) 

 and arbor vitee (Thuya) are interesting types to study comparatively with 

 the pine : (1) as regards the arrangement and forms of the leaves and conse- 

 quent appearance of the foliage ; (2) as regards the structure of the carpel- 

 late cones, whose scales are opposite instead of being distributed spirally, 

 and present other peculiarities of structure and habits of ripening ; (3) with 

 reference to the special characteristics of the stamens. These genera pre- 

 sent a higher type of gymnosperm evolution in these respects than the pine. 

 Certain cedars (Cupresaus) are equally good for this comparative study. 



THE ANGIOSPEEMS, OR ANGIOSPERM^ 



140. The morphology of the angiosperms. The general morphol- 

 ogy of the angiosperms, including roots, stems, leaves, flowers, 

 and fruits, together with many principles of plant physiology, 

 have been treated in Part I, The Structure and Physiology of 



