EVOLUTIONARY TENDENCIES AMONG GYMNOSPERMS 423 



mesozoic conifers. In fact, in certain living forms the sperms resem- 

 ble very closely those of cycads with cilia lacking. The abandonment 

 of ciliated sperms also affected the pollen chamber, the pollen tube, 

 and the cell generations in spermatogenesis. The pollen chamber 

 disappeared; the pollen tube ceased to be exclusively a branching 

 haustorial organ and became a sperm-carrier; while the last cell- 

 generation in spermatogenesis was omitted. It is this condition of 

 spermatogenesis that is carried forward by angiosperms to a still 

 greater stage of reduction. Just what cells are eliminated and what 

 cells remain is a question of small importance. The significant fact 

 is that spermatogenesis is shortened, and the ultimate cells, although 

 non-ciliated, are physiologically sperms. 



FERTILIZATION 



We have reserved for this topic, in addition to what it specifically 

 includes, a more detailed discussion of the sperm of gymnosperms and 

 certain related phenomena of spermatogenesis and oogenesis. Using 

 the term sperm in a physiological sense, what appears to be a reduc- 

 tion series can be arranged, extending from the highly differentiated 

 motile sperms of cycads and Ginkgo, presumably representative of 

 the sperms of the extinct groups, to the free male nuclei of Pinus. 

 Among the Taxodineae, Cupressineae, Taxineae, and Podocar- 

 pineae (certainly in Phyllocladus) the sperm is a distinctly organ- 

 ized cell ("male cell"). In such genera as Sequoia and Thuja 

 these male cells closely resemble the young sperms of a cycad 

 immediately after the division of the body cell. No vestiges 

 of blepharoplasts have been found in the so-called male cells, but 

 this negative evidence is not yet convincing. In every case, also, 

 they have been reported as arising directly by division of the body 

 cell, which means that they are not formed as sperms within a sperm 

 mother cell. It must be remembered, however, that apparently 

 competent observation maintained for a time this same origin for the 

 sperms of one of the cycads. Therefore, it is not an unreasonable 

 expectation that some of the male cells may be found to be formed 

 within sperm mother cells. In some genera, as Taxus and Torreya, 

 the two male cells have become unequal, one being much smaller 

 than the other and not functioning. The inference is that reduction 



