1909| COULTER—EVOLUTION AMONG GYMNOSPERMS 89 
phylls holding the same relation to one another that is held by the 
stamens and carpels of angiosperms; and this marks the Bennettitales 
as a unique group among gymnosperms. The monosporangiate 
tendency, however, which characterizes the coniferophytes, is shown 
by the Cycadales among cycadophytes, and it was either established 
directly, or it arose from an early differentiation of the amphispo- 
rangiate strobilus of the Bennettitales. The evidence of history 
favors the latter view, but the probabilities of the situation favor the 
former. In any event, both monosporangiate and amphisporangiate 
strobili were established among cycadophytes. 
THE STAMEN 
Among gymnosperms the stamen may be regarded as a very con- 
servative structure, retaining throughout most of the phyla its fern- 
like characteristics. Its form perhaps became almost as much 
differentiated among the Cycadofilicales as it ever became among 
gymnosperms. In this primitive group, in addition to microsporo- 
phylls resembling fern-like leaves with abaxial synangia, there 
appeared others that have been spoken of as the Crossotheca 
(“epaulet”) and the Calymmatotheca (“cupule”) types, and in 
all probability still others will be discovered. All of these types were 
continued among the coniferophytes, with varying details of minor 
importance. Among some of the Gnetales, either the sporophyll 
has become very much reduced, or it has become suppressed, so that 
the microsporangia are cauline; but even in Tumboa the old terminal 
synangium is evident. 
Among the cycadophytes, on the other hand, only what may 
be regarded as the most ancient type of microsporophyll has been 
retained, that is, the fern-type with abaxial sporangia (often syn- 
angia). Among the Bennettitales, there is so little departure from 
the old type that their microsporophylls resemble pinnate fern leaves 
with abaxial synangia; and even among the Cycadales the more or 
less leaf-like microsporophylls show the same character. If there is 
any tendency in the stamens of this phylum worth noting, it is the 
tendency shown among the cycads to reduce the sterile apex of the 
sporophyll to a more compact peltate expansion. 
The microsporangium of gymnosperms is a very consistent struc- 
