190 



PLANT STRUCTURES 



as in appearance, but they produce seeds and must be 

 associated with Spermatophytes, and as the seed is ex- 

 posed they are Gymnosperms. A discovery has been made 

 ______ _ recently that strikingly 



emphasizes their fern- 

 like structure. In fer- 

 tilization a pollen-tube 

 develops, as described 

 for pine and its allies, 

 but the male cells 

 (sperm mother - cells) 

 which it contains or- 

 ganize sperms, and 

 these sperms are of 

 the coiled multiciliate 

 type (Fig. 157) charac- 

 teristic of all the Pter- 

 idophytes except Club- 

 mosses. This associa- 

 tion of the old ciliated 

 sperm habit with the 

 new pollen-tube habit 

 is a very interesting in- 

 termediate or transition 

 condition. It should be 

 said that these sperms 

 have been actually found 

 in but few species of 

 the Cycads, but there 

 are reasons for suppos- 

 ing that they may be 

 found in all. Another 

 one of the Gymnosperm 

 groups, represented to- 

 day only by the com- 

 monly cultivated maid- 



Fio. 160. An araucarian pine (Araucarid), 

 showing the central shaft, and the regular 

 cycles of branches spreading in every direc- 

 tion and bearing numerous small leaves. 

 From " Plant Relations." 



