278 



THE AMERICAN NATURALIST 



[Vol. XL 



The facts just presented suggest the question whether the gym- 

 nosperms at the present time are in a process of retrogressive modi- 

 fication in the direction of the condition found in the pohen of the 

 angiosperms, or have the gymnosperms reached a condition of 

 stable equilibrium, not so much reduced as that of the angio- 

 sperms and with different groups of genera stable at different 

 stages in the reduction process. 



The mental attitude of those investigators who insist on labeling 

 a single prothallial cell as the second one implies a stable condi- 

 tion, with the number of cells formed invariable, and this mental 

 attitude seems to be the common one among the writers on the 

 subject. It seems to the present writer, however, that the number 

 and wide distribution of the variations found among the gymno- 

 sperms may indicate that the gymnosperms, or at least some of 

 them, are not in a state of stable equilibrium as regards the struc- 

 ture of the pollen grain, but that the process of reduction of the 

 male gametophyte is in progress. In Picea, for example, a very 

 few cases were found in which three vegetative prothallial cells 

 were seen, 15.7 % of the grains counted showed two, 66.5 % 

 showed one, and 3.8 % showed none. The number in others 

 was uncertain. In the case of the double pollen grains divided 

 into nearly equal parts, several showed no prothallial cell in one 

 part,, and a few showed none in either part. The extreme limits 

 of variation in the number of prothallial cells in the pollen grain 

 of Picea excelsa are therefore from to 3, with 1 as the number of 

 greatest frequency. 



These facts do not 'prove that Picea is in a condition of progres- 

 sive reduction of the male gametophyte, but at the very least they 

 allow that interpretation, and it is set forth merely tentatively. 

 Other investigations may either confirm or disprove it. Should 

 further investigations confirm this con(;lusion we should have a 

 Ciisc of a >trnf tiire clKmL^rd l)y gradual modification rather than 

 by iinifatioii. Tlu' occasi.mal \ ariations found in angiosperms 

 in whicli Hie |M)!l<>n u-raiii shows a vegetative prothallial cell, or 

 several inhv inich-i, or the sperniatogenous cell cut off at one side 

 of the grain instead of lying free in the cytoplasm of the tube-cell 

 (Coulter and Chamberlain, :03, p. 134-135) may possibly have 

 a similar significance. If so, the condition now found in the pollen 



