190 



PLANT STBDCTUKES 



^s^.- 



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 

 ^^^-^jr -^ ss^^j^^i,^^ ji_^ emphasizes their fern- 

 ^^^ 1 -.T^sE^ 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 

 havebeen actually found 

 in but two species of 

 the Cycads, but there 

 are reasons for suppos- 

 ing that they may be 

 found in all. Another 

 „ ,„„ , ■ ,A ■ X one of the Gymnosperm 



Fig. 160. An araucanan pme \Araucaria), *^ -^ 



Bhowing the central shaft, and the regular grOUps, represented to- 



cycles of branches spreading in every direc- ^^y Q^Jy '[jy |;Jjg COm- 

 tion and bearing numerous small leaves. — "^ i . 



Prom " Plant Relations." monly Cultivated maid- 



