144 



MORPHOLOGY OF SPERMATOPHYTES 



d'. 



modified strobilus, whose axis has become shortened and dilated 

 into a receptacle, resulting in a massing of bracts and axillary 

 sporangiferous shoots, the bracts in ripening organizing by 



their tips a continuous investment. 

 Whether this peculiar character of 

 the bracts represents a post-fertiliza- 

 tion change, or is developed before 

 pollination, is a question for future 

 discovery to answer. In any event, 

 the solitary cauline ovule, terminal 

 upon an axis of variable order, seems 

 to represent an ancient Gymnosperm 

 condition. 



From the testa of the seed it is 

 impossible to determine the nature of 

 the integuments. The testa is closely 

 adherent on the outside to the inclos- 

 ing and confluent tips of the bracts, 

 and shows three layers, the middle 

 one composed of very thick-walled 

 tissue, and much dilated toward the 

 micropyle. The innermost layer 

 forms the tubular micropyle, which 

 becomes somewhat dilated at the apex 

 and opens upon the surface of the 

 strobilus. It would appear that two 

 integuments are indicated, an inner 

 delicate one continued into the tubu- 

 lar micropyle, and a much heavier 

 outer one. The third or outermost 

 layer of the testa, which is closely adherent to the surrounding 

 bract tissue, may represent either an external layer of the outer 

 integument, or a limiting layer of the bract tissue. Such an in- 

 terpretation would conform in general with the structure of the 

 ovule in all the more primitive Gymnosperm types. 



Longitudinal sections of the seeds have also revealed a nu- 

 cellar beak and a large pollen chamber, which suggests Cordai- 

 tales, Cycadales, and Ginkgoales. One of the most striking 

 characters revealed by the seed, however, is the occurrence of a 

 large dicotyledonous embryo completely filling the embryo sac, 



FIG. 99. Bennettites Gribsonia- 

 nus, longitudinal section of 

 seed : a, the entering vascular 

 bundle; 6, its expansion at 

 base of nucellus ; c, the em- 

 bryo with two unequal coty- 

 ledons ; rf, the testa, terminat- 

 ing above in the tubular pro- 

 cess (r/), which leads to the 

 surface ; e, probably remains 

 of the nucellar beak, contain- 

 ing the pollen chamber. 

 After SOLMS-LAUBACH. 



