192 



MORPHOLOGY OF GYMNOSPERMS 



the mother cell stage before winter (47). Material collected during 

 April (in Ohio) by Miss Starr (53) showed some sporangia in the 

 mother cell stage and others with tetrads. 



The mature sporophyll has a rather long stalk, which terminates 

 in a knoblike enlargement, beneath one side of which usually two 

 pendent sporangia are borne. In material grown in the United 

 States there are often three or four sporangia; and Sprecher (47) 

 cites cases of stamens with as many as seven sporangia. Occasional 



_ abnormalities occur 



which show even 

 greater variation from 

 the usual form (fig. 

 218). The more or 

 less expanded knob 

 at the tip of the stalk 

 may be regarded as 

 representing a reduced 

 lamina bearing sporan- 

 gia pendent from its 

 abaxial surface. The 

 development of this 

 knob has been studied 

 by Miss Starr (53), 

 to discover whether it 

 gives such evidence of 

 abortive sporangia as 

 had been found in Torreya (40). The large mucilage cavities begin 

 to develop like sporangia, and for some time there is a close re- 

 semblance to sporogenous tissue, but finally the walls disintegrate 

 and a mucilage cavity is the result (fig. 221). The fact that the 

 stamen of Ginkgo sometimes bears more than two sporangia, and 

 that certain fossil forms bear more than two regularly, strengthens 

 the view that the mucilage ducts of the knob have replaced abortive 

 sporogenous tissue. At the same time, it is recognized that the 

 mucilage ducts elsewhere in Ginkgo, as in the leaves, pass through 

 the same developmental stages. 



Such a stamen suggests the Crossotheca ("epaulet") type among 



Fig. 218. — Ginkgo Mloba: dwarf shoot bearing nor- 

 mal strobili (_d), normal leaves (h), and leaves with 

 microsporangia (g). — After Fujil (17). 



