LIFE HISTORY OF PINUS 77 



and Gager ('02) show that the descendants of a pollen-mother- 

 cell in Ascleptas have a linear arrangement ; while Juel ('oo) 

 discovers that in the Cyperacece three young pollen-grains or 

 microspores abort and the fourth remains permanently within the 

 microspore-mother-wall. Yet from the standpoint of origin 

 alone, no one hesitates to call the young pollen-grains of these 

 plants microspores. Juel ('oo) affirms that the heterotypic divi- 

 sion must be the criterion by which we decide whether or.no we 

 have a true tetrad-division, and he concludes that in Larix the 

 embryo-sac-mother-cell is homologous with a spore or a micro- 

 spore-mother-cell. Schniewind-Thies ('01) reaches the same 

 conclusion for Angiosperms ; and Lloyd ('01) asserts that the 

 division of the embryo-sac-mother-cell in the Rubiacece is a 

 true tetrad-division, and the four resultant cells are spores. 

 Other instances where similar conclusions have been reached 

 might be cited, but the above is sufficient to demonstrate that 

 the most recent studies along this line point conclusively to a 

 normal spore-formation within the ovule, and do not confirm 

 Campbell's ('02) statement that a true tetrad-division is usually 

 absent in the ovule of spermatophytes. 



For many years botanists have been involved in a contention 

 regarding the true nature of the embryo-sac in Phanerogams. 

 A paper was published by Atkinson in 1901 reviewing the 

 interpretations made by earlier writers and suggesting as a 

 solution of the difficulty that spores, no longer being necessary 

 in the higher plants, had dropped out of the cycle of develop- 

 ment in these plants. That is, the female gametophyte arises 

 in the higher plants without the intervention of spores. While 

 the results of recent investigations do not serve to strengthen 

 this view, the theory is a most interesting one and the paper 

 has further served an excellent end in stimulating thought and 

 research along this line. Mottier observed one instance in 

 which the first division of the embryo-sac-mother-cell was homo- 

 typic, or, if we use Strasburger's ('oo) term adopted through- 

 out this paper, typical, and the number of chromosomes was not 

 reduced. Juel found the same to be true normally in Anten- 

 naria alpina, a species of Antennaria in which the embryo 

 develops parthenogenically. In both instances we have an 



