70 DUDLEY MEMORIAL VOLUME 



structure, conical in form, for a much longer time, and in so doing resemble 

 Anthoceros. For the reasons given above I cannot say that they would 

 always maintain this radial structure, though experience with these plants 

 and with Anthoceros leads me to believe that dorsi-ventrality, in these two 

 genera at least, is not alone inherited, but that it is a product of circumstances 

 as well as of substance, the continuity of substance and the continuity of 

 influence (direction of illumination) from generation to generation insuring 

 the repetition of this quality in successive generations. 



It may be suggested that the dorsi-ventrality does not develop in the 

 plants revolving on the turn-tables, not because it is not inherited, but because 

 it is prevented from appearing because one of the conditions for its devel- 

 oping is lacking. I do not care to contribute to a revival of the profitless 

 discussion, wisely dropped, involving a conceivable if unnecessary distinction 

 between condition (Bedingung) and stimulus (Reiz), for, as will more 

 plainly appear in the next section (pp. 70-74), the influence of the direction 

 of illumination is active rather than passive. When one compares, at the 

 end of an experiment which has lasted for months, the sizes of the plants on 

 the turn-tables with those on the shelf, one realizes the greater size of those 

 more uniformly illuminated, symmetry and size going together. 



The result of growing Fimbriaria Calif arnica from the spore under con- 

 ditions of equal and of unequal illumination from all directions successively, 

 is the same, so far as the experiments could be continued, as with the two 

 species of Anthoceros previously reported upon, but the longer life-cycle of 

 Fimbriaria makes it necessary to continue the experiment for a longer time 

 than has so far been possible, in order to reach a definitive result and to 

 justify a final conclusion. Fimbriaria grown from the spore does not fruit, 

 at least in my cultures, within the time limits of one natural growing season 

 that is, between the first rains, say early in November, and the beginning of 

 the dry season, in May. On the other hand, Anthoceros does, but its spores 

 are not equally fertile in successive seasons, and since the wonderful crop of 

 1905 I have been unable to secure spores of such vigor that I cared to con- 

 tinue experimenting upon the plantlets beyond confirming previous results. 

 Nor is it necessary, as the results reported in the next section will show. 



Pteris aquilina and Gymnogramme triangularis. 



Spores of Pteris collected in southern California in June, and of Gym- 

 nogramme collected near the laboratory in September, were sowed on October 

 11, 1911, under the conditions previously described. Six of the cultures of 

 Pteris were set on turn-tables revolving four times a minute, two on the shelf 



10 Peirce. Ann. Bot., 1906. 



