CONIFERALES (PINACEAE) 277 



sperms, are called for convenience simply male cells. The dis- 

 appearance of the wall between the two male cells, leaving the male 

 nuclei free in the cytoplasm of the body cell, represents a further 

 stage in the reduction of the male element. The significant fact is 

 the abandonment of the swimming sperm by Coniferales, and when 

 one recalls the surprising persistence of swimming sperms in con- 

 nection with the land habit, their final disappearance marks an 

 epoch in the history of land plants. With the abandonment of 

 swimming sperms, blepharoplasts in the body cell have disappeared, 

 and the pollen tubes are utilized as sperm carriers. 



The appearance of two evanescent vegetative (prothallial) cells 

 is a feature only of the Abietineae, and even among them there is 

 some fluctuation, the spores of Picea excelsa having been observed 

 (114) to produce one to three such cells. Among Taxodineae and 

 Cupressineae no such cells occur, the vegetative tissue of the male 

 gametophyte having been eliminated completely. In these tribes, 

 therefore, the first division of the pollen grain produces the generative 

 and tube cells. The ephemeral nature of the prothallial cells in 

 Abietineae suggested for a time that they had escaped observation 

 in the two other tribes, but the evidence is now too complete to warrant 

 any such assumption. Among Taxodineae the absence of prothallial 

 cells is known for Sciadopiiys (175), Cunninghamia (147, 180), 

 Sequoia (64, 92), Cryptomeria (85, 93), and Taxodium (76); and 

 among the Cupressineae it is known for Callitris (85), Widdringtonia 

 (159), Libocedrus (131), Thuja (72, 86), Cupressus (85), Chamaecy- 

 paris (85), and Juniperus (85). Since this list includes twelve 

 genera of the eighteen included in the two tribes, there is no reason 

 to expect that vegetative cells will be found in the remaining genera. 

 In this feature, therefore, the Abietineae are in a more primitive 

 condition than are the two other tribes. 



Among Araucarineae, however, there is still another prothallial 

 situation (figs. 319-321). Two lens-shaped vegetative cells are cut 

 off, as among Abietineae, but they are not ephemeral. Lopriore 

 describes them (104) in Araucaria Bidwillii as giving rise to a tissue 

 of about fifteen cells, whose walls presently disappear, freeing the 

 nuclei, which then continue division, until twenty to forty-four (most 

 frequently thirty-six) free nuclei were observed, no divisions occurring 



