SPERMATOPHYTA 



337 



Fig. 287. Ovulate strobili of Ginkgo biloba. A, dwarf shoot bearing cluster of young 

 leaves and ovulate strobili, two-fifths natural size; B, enlarged view of three strobili, each 

 bearing two ovules. 



Fig. 288. Ginkgo biloha. A, longitudinal section of young ovule, showing "collar," 

 integument, nucellus, and spore tetrad, X15; B, enlarged view of tetrad of niegaspores 

 surrounded by nutritive tissue, X400. 



Ovulate Strobilus. The ovulate strobili are greatly reduced. Each 

 consists of a long stalk that bears mostly two terminal ovules, only one of 

 which ordinarily matures as a seed (Fig. 287). At the base of each ovule 

 is a peculiar "collar." This probably represents a vestigial megasporo- 

 phyll, since in rare instances it may become leaf-like. Sometimes three 

 or four ovules may be boVne on the same stalk. The ovule is character- 

 ized by a single massive integument. As in the Cycadales, this is three- 



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