1916] JEFFREY & TORREY—GINKGO 291 
2. A similar condition of relationship between the tracheary 
tissues and the dehiscing mechanism of the microsporangium is 
likewise found in the Abietineae among the conifers. 
3- In the remaining conifers (and including the araucarians) 
the sporangial mechanisms are much reduced and no longer have 
a eee to the vascular bundles of the sporophyll. 
. In the angiosperms the fiber layer of the anther wall is 
italy well developed and is of internal origin, but has no connec- 
tion with the fibrovascular system, even in the forms regarded 
as low. 
5. From the Cycadales downward the opening mechanism of 
the sporangium is of the nature of an annulus and is epidermal 
in its origin. 
6. The facts sainmearies under the foregoing headings justify 
the separation of reproductive mechanisms in the vascular plants 
into two types, the ectokinetic and endokinetic. The former condi- 
tion is represented by the annulus and is characteristic of lower 
forms; the latter is found in the fiber layer, derived from the 
fibrovascular tissues (particularly modified transfusion elements), 
and is present characteristically in the microsporangia of existing 
seed plants (exclusive of the Cycadales). 
HARVARD UNIVERSITY 
EXPLANATION OF PLATES VII-IX 
PLATE VII 
Fic. 1.—Vertical section through upper part of sporophyll of Ginkgo 
biloba, showing relation of mechanical elements of wall of sporangium to 
transfusion cells and fibrovascular bundle; 
Fic. 2.—Vertical section of snothersdorh hehe showing the same features; 
X 150. 
G. 3.—Horizontal section showing relation of two fibrovascular bundles 
to a tissue and mechanical elements; 100 
Fic. 4.—Part of the right of fig. 3 more highly magailied, showing merging 
of sietabcad elements into mechanical elements; X 200 
Fic. 5.—Vertical section of sporangium of abi. showing termination 
of bundle in transfusion elements and mechanical cells; X 150. 
Fic. 6.—Vertical section of sporangium of Ginkgo, showing termination 
of bundle in transfusion elements and mechanical cells; X 250. 
