THE PINE 151 



D. The gametophytes. The germination of the spores of Isoetes and tlic 

 development of the gametophytes is even more difldcult to follow than 

 that of Selaginella and requires detailed study. 



Reference. Campbell, 23. 



THE GYMNOSPERMS, OR GYMNOSPEKM^ 



137. Cycads. Cycas revoluta is a large form frequently cultivated in park 

 conservatories, and may be used to illustrate the general morphology of the 

 cycads, that is, the trunk-like, unbranched stem bearing the crown of com- 

 pound leaves at the top. This cycad occasionally develops sporophylls in 

 the greenhouses, which may then be collected and preserved for study. 

 The carpels are developed more commonly than the stamens. 



Zamia is a small cycad which grows in Florida and is an admirable type 

 for a study of the cycad cone, together with the development of the ovules 

 and pollen, the structure of the male and female gametophytes, processes of 

 fertilization, and development of the embryo. Cones of Zamia may be readily 

 shipped, and since the ovules retain their vitality for a considerable time 

 they can be studied alive in the North or killed and preserved for micro- 

 tome sections. Zamia may also be readily grown from seed in greenhouses, 

 and will produce cones under cultivation. Its study is recommended wher- 

 ever possible. 



138. The pine (App. 21).. Several species are available for this 

 study, such as the Scotch pine (Finns sylvestris), the Austrian 

 pine (P. laricio), F. Strobus, F. palustris, or some of the scrub 

 pines, such as F. Banksiana. Living material for general mor- 

 phological or histological work may be obtained at any time of 

 year. The young cones should be collected and preserved in alco- 

 hol at the time of pollination in May, when the year-old cones 

 may also be gathered and preserved for comparison with the 

 first. Dried, open cones and seeds should be collected in the late 

 summer or autumn. The pine should also be studied in the field 

 to determine its growth habits and the ecological adaptations of 

 its foliage to conditions of severe cold and drought. 



A. General morphology. Observe : 



1. The main stem and hranchrs^ eacli ending in a terminal 

 hud ; the arrangement of the branches. 



