362 



THE A M ERIC AN NA T URA LIST [A^ol. XLI 



Cycads and Ginkgo there are one or two prothallial cells present. 

 The generative cell undergoes only a tangential or periclinal 

 division in connection with the formation of the stalk cell and 

 antheridial cell. The antheridial cell in both the Cycadales and 

 Ginkgoales gives rise to two spermatocytes, the mother cells of 

 antherozoids. In the Abietinete, which we know from the 

 evidence of the fossil remains extend very far back geologically 

 in forms allied to Pinus, there are two evanescent prothallial cells 

 present in the mature microgametophyte, and a generative cell 

 which as in the zoidogamous Gymnosperms gives rise to stalk and 

 antheridial cells by periclinal division. The antheridial cell in turn 

 gives rise to two cells which are to be regarded as the homologues 

 of the two spermatocytes of the Cycadales and Ginkgoales. In 

 the Araucarineae, so far as our knowledge goes, there are formed at 

 first two prothallial cells, which may subsequently undergo more or 

 less numerous anticlinal and possibly also periclinal divisions. 

 The final history of the generative cell is obscure, but it is to be 

 inferred from the brief summary of Thomson (loc. cit.) that the 

 antheridial cell of the Araucarinete does not divide into two as in 

 the AbietinctT and the ancient zoidogamous Gymnosperms. In 

 the Araucarine£e there is a further remarkable feature in that the 

 pollen grain does not reach the micropyle of the ovule as in the 

 other Coniferales and all other known Gymnosperms living or 

 fossil; but is deposited on some part of the ovuliferous scale or 

 megasporophyll (on the 'ligule' in Araucaria) thence sending a 

 pollen tube down to the ovule, in a manner analogous to that 

 obtaining in the Angiosperms. Thomson, adopting the prevailing 

 hypothesis that the Araucarinese are the most primitive Coniferales, 

 designates this peculiar mode of fertilization as primitive or ' pro- 

 tosiphonogamic' 



This view presents some difficulties, for if the quasi-angiosperm- 

 ous method of fertilization found in the Araucarinese is ' primitive ' 

 it is difficult to see why such a method is entirely absent in the 

 older g),'mnospermous series, the Pteridospermje, Cordaitales 

 and Ginkgoales, or being ancestral for the Coniferales is entirely 

 lost in the coniferous families other than the Araucarineae, which 

 have moreover a method of pollination resembling closely that 

 of the older Gymnosperms in that the microspores are received 

 through the micropyle. The reported presence of only a single 



