396 



BOTANY. 



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

 The exceptions, which are in the order Gnetaceae, 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. 



FIG. 287. 



Fig. 285. A, pollen grains of Biota vrientalis before their escape from the pollen 

 sac ; 7., fresh ; II. and ///., after lying in water, the extine, f, having been stripped 

 off by the swelling of the inline, ; the protoplasmic contents are seen to consist 

 of two cells, a large nucleated one, and a smaller one. S, pollen grains of Pinug 

 pinaster, before their escape Irom the pollen sac ; f, extine, with its vesicular protru- 

 sions, bl; IV., side view; V.. dorsal view the protoplasmic contents are divided 

 similarly to those in A. Magnified. After Sachs. 



Fis. 286. A, a pollen grain of Cufirestru-n semperrirens, 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 Schaeht. 



Fig. 287. Pollen grains of Ceratozamia lonyi folia. A, before permutation ; y, 

 a three-celled body, the rudimentary prothalliuni" H. a germinating pollen grain ; e, 

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

 After Juriinyi. 



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 (bl, Figs. 285, B, and 281, B), which are common in 

 certain genera of the order Conifera, 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 



