iqiq] dupler—taxus 353 



is in marked contrast with the behavior in the related Torreya, in 

 which a resin cavity results from the abortion of some of the poten- 

 tially sporogenous tissue of the sporophyll, the abortion beginning 

 at the primary sporogenous cell stage, as pointed out by Coulter 

 and Land for T. taxijolia. This results in the sporangia occurring 

 on only one side of the otherwise peltate sporophyll. Miss Robert- 

 son also finds that normally there are 4 sporangia on the side of the 

 sporophyll of T. calif ornica and a resin cavity on the other side, but 

 that the strobilus axis sometimes terminates in a radially sym- 

 metrical sporophyll, like that of Taxus, with 6 or 7 mature 

 sporangia. Whether a resin cavity is present in such a sporophyll 

 is not stated, the inference being that most or all of the sporangium 

 initials reached maturity. A similar abortion of sporangia, in the 

 formation of mucilage cavities, is indicated by Miss Starr's (21) 

 work on Ginkgo biloba. Coulter and Land find in Pinus Laricio 

 resin cavities related to sporangia, exactly as are the lateral 

 sporangia to the two middle ones in Torreya, and say "there is 

 evident a tendency to reduce the number of sporangia by abortion, 

 a reduction that has proceeded farther in Pinus than in Torreya, 

 and in the latter farther than in Taxus." It seems that when resin 

 or mucilage cavities are present in the sporophyll the sporangium 

 initials are involved, and when absent these initials may all function 

 normally, as in Taxus. Whether this can be made as a general 

 statement for all forms with resin cavities in the sporophyll must 

 wait for more extensive work on other forms. Cephalotaxus has a 

 sporophyll similar in general appearance to that of Torreya, but it 

 is not known whether any abortion takes place. 



Sporangium wall. — The initial development of the wall is 

 from the primary wall cell, which by a periclinal division forms a 

 tier of 2 cells. As the sporogenous tissue develops, these wall cells 

 divide anticlinally (fig. 31), increasing the extent of the wall layers. 

 Only a portion of the wall is derived from the primary wall cell, 

 however, as other cells abutting the young sporogenous tissue divide 

 periclinally and add to the wall, first on the outer side (figs. 31-33) 

 and then on the inner side as well (fig. 34), thus completely envelop- 

 ing the young sporogenous tissue. The wall usually consists of 

 2 layers of cells, although 3 or even more layers may be present, 



