OTMNOSPERM^. 



397 



same figure. ) In all cases, unless possibly the Gnetaceas fur- 

 nish some exceptions, the pollen grains become more than one- 

 celled before the formation of the pollen tube (Figs. 281-5- 

 6-7). When the pollen grains germinate i.e., send out their 

 tubes they always swell up and 

 burst the extine (which slips off 

 in the Coniferae), and the intine 

 is then prolonged into a tube, 

 which is continuous with the 

 cavity of the grain, and into 

 which the protoplasmic con- 

 tents pass (Figs. 286 and 287). 

 The small cells take no active 

 part in the formation of the 

 tube, and from their similarity, 

 both in structure and function, 

 to the small cells in the germi- 

 nating microspores of the Sel- 

 aginellm, there can be no doubt 

 that they are to be regarded 

 as constituting a rudimentary 

 prothallium. 



509. The female flower is 

 in most cases a similar elon- 

 gated axis, upon which are ar- 

 ranged spirally a considerable 

 number of phyllomes, each 

 bearing two or more naked ov- 

 ules. Thus in Abies pectinata 

 the female flower is the young 

 cone, which consists of an axis 

 (sp, Fig. 288, B} bearing nar- ovulefi '*< enlar g ed )- #, upper pan <>f 

 row bracts (c), which, in turn, b^c^^hS^Sa^ 

 develop thick scales (s, s) upon %*%% ^K^JSS; 

 their upper surface. The scales scnacht. 



are at first quite small (as in A), and it is only as the cone 

 becomes older that they grow larger. Each scale bears on 

 its inner face two inverted ovules (sk, Fig. 288, A). 



In Pinus sylvestris the structure is essentially the same as 



Fig. y.-A. a bract, e , detached 



