DEVELOPMENT OF PLANTS 367 



would doubtless become extinct. The gymnosperms, however, 

 live in colonies and the strobili of mega- and micro-sporophylls 

 usually occur upon the same plant, thus necessitating but a short 

 transfer of microspores. The megasporophylls usually endure 

 for a year or more and become quite large, forming the leathery 

 or woody scales of the cone- or strobilus (Fig. 252). The mega- 

 sporangia are usually developed on the upper side of the sporo- 

 phyll (Fig. 253, A), the number formed varying in the different 

 genera. In the majority of the Pinales, the sporangia appear 

 upon curious outgrowths which become large and form the 

 conspicuous scales of the cone. This structure is generally 

 regarded as a greatly modified branch or shoot with which two 

 sporophylls are fused. It generally arises from the axil of a 

 bract just below it and with which it may be more or less united — 

 see the spruces, pines, firs, etc. (Fig. 253, B). The origin and 

 structure of the megasporangium and megaspore are essentially 

 as noted in the cycads. There is only slight indication, however, 

 in a few of the forms of the development of a cavity for the 

 reception of the microspores. Several mother cells may form 

 megaspores, but only one of these megaspores ever develops and 

 germinates. 



(c) The Gametophyte of the Pinales and Fertilization. — The 

 female gametophyte is formed as previously noted in the cycads. 

 By the repeated divisions of the nucleus of the megaspore numer- 

 ous free nuclei are formed that become arranged around the walls 

 of the megaspore. Later cell walls are developed about these 

 nuclei, and by further division the entire space within the enlarg- 

 ing spore is filled with tissue (Fig. 253, C). A few or a large 

 number of archegonia are developed at the micropylar end of 

 the gametophyte. The archegonium consists of two or several 

 neck cells, and a large female gamete which is surrounded by 

 nourishing cells as in the cycads. It is noteworthy in a few of the 

 forms that the archegonia begin to appear very carl>' in this 

 growth outlined above and that the bulk of the female gameto- 

 phyte is developed subsequent to their origin. The possible 

 significance of this will be more apparent in the Angiosperms, 

 where we will see the female gamete arising with the third division 



