1916] JEFFREY & TORREY—GINKGO 285 
sporangium from the Stephanian of Grand’ Croix in France. He 
notes that in the sporangium in question, which he is inclined to 
refer to the Botryopterideae, there are 6 islands of tracheary tissue 
lying in immediate contact with the cavity of the sporangium. 
A true annulus formed from the outer layer of cells likewise is 
present, and consequently there can be no case of vascular tissue 
acting as the mechanism for opening the sporangial cavity at 
maturity. The author notes the rarity of the phenomenon in 
vascular plants, where as a rule the tracheary elements stop at an 
interval from the actual sporogenous elements. He calls attention 
to the similar phenomenon presented by the tracheids found in 
relation to the embryo sac in the amentiferous genera Casuarina, 
Castanea, and Corylus. In a later articlet OLIvER describes the 
tracheary investment covering the gametophytes and terminating 
in the pollen chamber of Stephanospermum akenoides and S. | 
caryoides. He regards the apparatus in this case as destined to 
supply the pollen chamber (a constant feature of organization of 
more ancient gymnospermous seeds) with the water necessary to 
provide for the fertilizing movements of the antherozoids possessed 
by these extinct types in common with their nearest modern sur- 
vivors Ginkgo and the Cycadales. In the living forms, however, 
the tracheary device for supplying fluid to the pollen chamber has 
disappeared. It is of interest to note in the present connection 
that in the megasporangium (or seed) of Ginkgo the transfusion 
tissue is present in the peduncle of the organ just as it is in the 
Stalk of the microsporangium, but that it dies out sharply as the 
megasporangium proper is reached. It is present in abundance 
in the collar, which lies against the base of the seed. The sporan- 
gium in Ginkgo would seem, in view of the present observations, to be 
more tenacious of ancestral characters than is the megasporangium. 
It is now desirable to consider certain general features of organi- 
zation of the wall in the sporangia or microsporangia of the lower 
vascular plants. Fig. 13 illustrates the structure of a sporangium 
of Polypodium vulgare. Here the opening mechanism is provided 
4 Outver, F. W., On the structure and affinities of Stephanospermum Brongniart, 
@ genus of fossil gymnospermous seeds. Trans. Linn. Soc. London Bot. IT. 6:361-400. 
bls. 41-44. 1904. 
