DEVELOPMENT OF PLANTS 335 



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 case of many of the Pinales, the sporangia appear 

 upon curious outgrowths of the sporophyll which become large 

 and form the conspicuous scales of the cone, while the sporophyll 

 proper appears as a small bract just below it, as in spruces, pines, 

 firs, etc. (Fig. 253, B). The origin and structure of the mega- 

 sporangium and megaspore are essentially as noted in the cycads. 

 Several mother cells may form megaspores, but only one of these 

 megaspores ever develop and germinate. 



(c) The Gametophyte of the Pinales and Fertilisation. 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 nour- 

 ishing cells as in the cycads. You notice that there is no cham- 

 ber formed above the archegonia, and it would be a natural infer- 

 ence that the male gametophyte must be of a somewhat different 

 character from that of the cycads in order to meet this new de- 

 parturey The microspores which have already begun to germi- 

 nate when discharged from their sporangia are carried by the 

 wind to the megasporophylls which are slightly spread apart at 

 this time, permitting the microspores to rattle down to the mega- 

 sporangia. The microspores fall into the micropyle either by 

 reason of the position and construction of the megasporangia, 

 which may be so placed that the spores naturally roll down into 



