396 



BOTANY. 



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

 The exceptions, which arc in the order Gnetaceffi, will be de- 

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

 ing up througli 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. 



Pig 286. 



Pig. 287. 



Pig. 285.— -4, pollen gr-iins of Bioia orienfnlia before their escupc rrom the pollen 

 eac \ /., ft-esh ; //. anrl ///.. after lying in water, the exiine, €, hnving been Biripped 

 off by the swelling of the intine, i ,• the protoplasmic contents are seen to consist 

 of two cells, a large nucleated (>nc, and a smaller one. B, pollen grain* of H-niis 

 pinaster^ before their escape Ironi the pollen sac ; e, extine, with its vesicular protru- 

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

 similarly to those in A. Magnifli-d.— After Sachs. 



Pis. 286. — A, a pollen grain of Ouj/ressnis eempej^irens, 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 rnptured and 

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



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

 a three-celled body, the rudimentary prothallium. B. a germinating pollen grain ; c , 

 the ruptured extine ; ji8, the pollen tube ; y, rudimentary prothalnum. 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 {hi, Figs. 285, B, and 281, B), which are common in 

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

 close similarity which exists between the pollen grains iu 

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



