396 



BOTANY. 



is in nearly all the class essentially like the ones described. 

 The exceptions, which are in the order Gnetacese, will be de- 

 scribed further on. It may be pointed out here that in pass- 

 ing up through the three orders of the class, the pollen sacs, 

 which in the first resemble sporangia, become more nearly 

 like the anthers of the Monocotyledons and Dicotyledons. 



Fig. 285. 



Fig, 286. 



FiQ. 287. 



Fig. 985. — A, pollen grains of Biota orientMis before their escape from the pollen 

 eac ; 7., fresh; II. and III,, after lying In water, the extino, c, having been stripped 

 off by the swelling of the intine, i ; the protoplaBmic conteiitp are seen to consist 

 of two cells, a large nucleated one, and a smaller one. B, pollen grain=i of Finus 

 pinasfer^ before their escape Irom tlie pollen sac ; e, extine, witli iis vesicular protru- 

 sions, bi ; IV., side view ; Fi, dorsal view — the protoplasmic contents are divided 

 similarly to those in A. Magnified. — After Sachs. 



Fiir. 286. — A, a pollen grain of Cupressua eempervirerts, showing the envelopes (ex- 

 tine and intine), and the rudimentary prothallium as a small cell cut off from the 

 cell contents. B, a germinating pollen grain ; e, the fragments of the ruptured and 

 exfoliated extine ; i, intine ; tp, the base of the pollen tube. X 400.— After Schacht. 



Fig. 287. — Pollen grains of Ceratozamia longifolia. A, before germination ; y, 

 a three-celled body, the rudimentary prothallinm. B, a germinating pollen grain ; e, 

 the ruptured extine ; ps, the pollen tube ; y, rudimentary prothallium. Magnified. 

 — After Juranyi. 



508. — The pollen grains, like the male flowers themselves, 

 are essentially alike, although differing considerably in ex- 

 ternal appearance. The vesicular protrusions of the ex- 

 tine (II, Figs. 285, B, and 381, B), which are common in 

 certain genera of the order Coniferm, at first sight hide the 

 close similarity which exists between the pollen grains in 

 many cases. (Compare A,_I., in Fig. 285, with B, IV. of the 



