28o 



GYMNOSPERMS 



What causes the changes in sex characters has not been deter- 

 mined for either gjTnnosperms or angiosperms. These peculiarities 

 have been noted more frequently in exotic individuals; but whether 

 the conditions are more likely to occur in such cases, or such cases 

 are more likely to be noticed, might be questionable. It has been 

 claimed that abnormalities occur more fre- 

 quently in nursery material: it is certain 

 that they would be more likely to be noticed. 

 Comparatively little histological work 

 has been done in this field, nearly all the ac- 

 counts dealing with mature cones. It would 

 not be impossible, or even very diftkult, to 

 collect a series in various stages of develop- 

 ment, for a tree which produces teratolog- 

 ical cones produces them year after year. 



In the most frequent teratological cases 

 the arrangement of staminate and ovulate 

 sporophylls on the cone a.xis resembles a fre- 

 quent arrangement of staminate and ovu- 

 late strobili on a tree; for the ovulate cones 

 are higher up, with the staminate lower 

 down, as in Abies. In Piniis it is very rare 

 to see a staminate cone at the top of a tree 

 or tip of a branch, while this is the usual 

 place for ovulate cones. In seasons in which 

 scarcely any cones are produced, two or 

 three ovulate cones can usually be found at 

 the top of the vertical shoot at the extreme 

 top of the tree. In Saxagothea the ovulate cone is terminal on a short 

 branch, which bears staminate cones farther back in the axils of its 

 leaves. In general, the ovulate cones are more numerous at the top 

 of the tree or at the ends of the branches, with staminate cones far- 

 ther down or farther back on the branch, suggesting the arrange- 

 ment in the bisporangiate angiosperm flower. 



Fig. 283. — Pinus mari- 

 tima: bisporangiate strobi- 

 lus. The lowest three spo- 

 rophylls on each side bear 

 microsporangia; the next 

 sporophyll above, on each 

 side, has a microsporan- 

 gium in the lower part and 

 a rudimentary ovuliferous 

 scale in the axil; above 

 these are ordinary ovulif- 

 erous structures. — After 



GOEBEL.'" 



THE STAMINATE STROBILUS 



Throughout the entire order, the staminate strobilus is simple, the 

 sporophylls being borne directly upon the cone axis. There are no 



