iQiq] 



DUPLER—TAXUS 355 



some points. The meristematic ability, however, soon becomes 

 limited to the base of the sporangium, the epidermal cells of the 

 remainder of the sporophyll becoming larger and with less dense 

 contents, the cells at the base remaining isodiametric and rich in 

 cytoplasm (figs. 32-34). As the sporangium increases in size, 

 causing a more pronounced lobing of the sporophyll, the necessary 

 increase in epidermal surface is effected by the enlargement of the 

 non-meristematic cells and the addition to them of cells from the 

 basal meristematic region. The enlarged cells become filled with 

 an amorphous substance and the walls become thicker. 



By the time the sporangia are mature the epidermis has become 

 the functional wall of the sporangium, owing to the practical dis- 

 integration of the true sporangium wall. At maturity the epidermal 

 cells are devoid of contents and have the markings characteristic 

 of the walls of many sporangia (figs. 11-12), these thickenings 

 exercising a hygroscopic effect, useful in the liberation of the spores. 

 Jeffrey (12) regards this thickening of the epidermal cells of the 

 sporophyll, in a mechanical dehiscing device, as the result of the 

 invasion of the epidermis by mechanical tissues of fibrovascular 

 origin. There are no indications in Taxus of mechanical elements 

 elsewhere in the sporophyll. Coulter and Land found numerous 

 stomata in the epidermis of Torreya. In Taxus canadensis there 

 is a single stoma on a sporophyll, at the center of the peltate disk, 

 occupying the bottom of the depression caused by the enlarged 

 sporangia (fig. 10). Goebel (10) shows a similar situation in 

 T. baccata. 



Mature strobilus 



The scales at the base of the strobilus are small and decussate, 

 increasing in size and becoming spiral in arrangement above, the 

 uppermost ones being considerably larger than the lower ones, and 

 function as bud scales in the immature condition of the strobilus. 

 The scales are brownish in color, with heavily cutinized outer 

 epidermal walls, especially on the abaxial surface, the stomata 

 occurring only on the inner surface (fig. 37), reversing the condition 

 on the vegetative leaves of the plant, where the stomata occur only 

 on the lower (abaxial) surface. The midrib is marked by the 



