CERTAIN STEUCTUEES IN THE GENUS GNETUM. 313 



tlie upper part of the spike {i. e. androgynous of G. Gnemon) breaks off and falls to the 

 ground, leaving the flowers of the lowest axils." In the first case found there were two 

 such flowers at the lowest node ; one had three envelopes, the other four (figs, 2, 3j ; each 

 contained more than one embryo-sac, all in an early free-nucleate condition. The 

 former contained many pollen-grains in the micropyle; two of these are shown in 

 detail in fig. 9. This node "bore no incomplete female flowers ; these were, however, 



present in their usual position at the upper nodes. 



This observation is of interest, in that it undoubtedly explains the statements of 

 previous authors referred to above. Since these ovules do become pollinated, it may be 

 presumed that fertilization ensues in some cases at least and that fertile seeds may be 

 borne upon the spikes w^hich produced the male flowers. In other words, in Onetiim 

 Gnemon, as probably also in G. Leyholdi and other species, there is found a truly 

 androgynous as well as a pseudo-androgynous spike. 



The four types of spike now described establish a sequence ranging from the strictly 

 unisexual to the bisexual, or conversely, which leaves no doubt that the two commoner 

 types are members of the same evolutionary series. Whether this series progressed in 

 two directions from a primitive bisexual form or from two unisexual inflorescences 

 towards a combined type, has been a fruitful subject for discussion. Wcttstein "^ 

 holds the latter view for all the genera of the Gnetales. The principal points in his 

 argument are the following : 



1. The primitive flower of the Gymnosperm was unisexual. Bisexual inflorescences 



are unknown in the Gycads, but are relatively common in the higher forms. 



2. EpJiedra campylopoda (the only member of the genus in which a bisexual 



inflorescence occurs at aU commonly) does not, in its general characters, give 

 the impression of being a primitive form. 



3. The archegonia of the female flower of the androgynous spike of G. campylopoda 



show no signs of reduction, although they apparently do not become 



fertilized. 



4. If the occurrence of $ flowers in this androgynous inflorescence is really due 



to reversion, then a similar reversion would be expected to occur in the 



$ inflorescence. 



5. If, on the otlier hand, the appearance of bisexuality is due to " progressive 



mutation " (as Wettstein believes), then it would be expected to appear in 

 the c? inflorescence rather than in the $, on account of the normally 

 unlimited growth of the former. 



Wettstein quotes the evidence of Blurae, Griffith, and Lotsy as to the occasional 

 appearance of a bisexual inflorescence in Gnetum, and is inclined to think that "auch 

 morphologisch diese ' zweigeschlechtigen ' mannlichen Bliiten von Welicitschia analog 

 erkliirt werden konnen, wie die zweigeschlechtigen Infiorescenzen bei Ephedra." 



These arguments are not convincing. No. 1 would have greater force if the living 



»> 



Gymnosperms formed a monophyletic group. The history of certain sections of the 



• Wettstein, 1907, p. 28. 



2z2 



