CONIFFRM. • ' S^5 



is developed from a group of superficial cells : these multiply by repeated division, 

 so that a protuberance is formed consisting of a number of rows of cells invested 

 by a parietal layer: the terminal cell of the lowest of these rows becomes the 

 archesporium, and it is therefore, in this case also, a hypodermal cell. The cells 

 of the tapetum are derived entirely from the parietal cells of the pollen-sac, just 

 as is the case in the sporangium of Lycopodhim. Goebel draws attention to the 

 fact that in the majority of the Cupressineae the pollen-sacs are protected by an 

 outgrowth of the staminal leaf which he considers to be analogous to the indusium 

 of Ferns.] 



A formation of cells, recalling the rudimentary development of a prothallium 

 in the microspores of Selaginella and Isoetes, takes place in the pollen-grains of 

 the Coniferae before their dissemination, in the same manner as in those of the 

 Cycadeae (compare Fig. 3^). The process is a very simple one in Taxus 

 Podocarpus, the Cupressineae, Araucaria and in the true Pines. The contents of 

 the pollen-grain are divided by a septum so as to form a large and a small cell, 

 the latter undergoing no subsequent change (Fig. 351). In the other Abietineae 

 the septum becomes arched into the cavity of the larger cell, and a second septum 

 is formed in the smaller cell, so that a two-celled body is formed which is situated, 

 as in the Cycadeae, at the posterior end of the grain. At this point the extine 

 presents a split which was formerly regarded by Schacht as being the basal cell 

 of the internal group, but which, according to Strasburger, arises in the same 

 way as the vesicular expansions of the extine found in the grains of many species 

 of Pinus. Strasburger has shown that in all cases it is the large cell cf the 

 pollen-grain which grows out into the pollen-tube, as is the case in Cycadeae 

 (Fig. 345). If we pursue the comparison with the highest Cryptogams which 

 has been already initiated, we must regard the pollen-tube as representing the 

 antheridium to some extent, and the internal group of cells, formed before the 

 development of the pollen-tube, as corresponding to the vegetative cell in the 

 microspore of the Ligulatae, for, like it, it undergoes no subsequent change. A 

 peculiarity which distinguishes the pollen-grain of Conifers from that of Angiosperms 

 lies in the rupture and final stripping off of the extine by th^ swelling of the 

 intine (Fig. 351, /, //, ///). Even in this apparently insignificant fact a resem- 

 blance is again seen to the microspores of Cryptogams, and especially to those of 

 Marsiliaceae, in which the swelling endospore protrudes through the exospore. 



The structure of the Female Flowers is very different in the different sections of 

 Coniferae, and in some cases the homology of the separate parts is still doubtful. 

 The position of the ovules, as far as can be judged from advanced stages of develop- 

 ment, is, in particular, very variable, and with this is again connected the fact that 

 different opinions may be entertained as to the part which should be called the 

 carpel. The following description of these structures, a full discussion of which is 

 not permitted by our limited space, is drawn immediately from the observation of 

 advanced stages of development ; it is possible, however, that the direct observations 

 of the most rudimentary stage will cause an alteration in some points ^ 



The female flowers of Taxus spring from the axils of foliage -leaves belonging 



Compare Strasburger and Eichler, loc. cit. 



l1 2 



