156 MORPHOLOGY OP SPERMATOPHYTBS 



strong tap root is to be noted ; while the peculiar origin of the 

 root cap seems to distinguish the group as a whole from Angio- 

 sperms. There is no distinct calyptrogen, but the periblem 

 layers are continuous over the tip, and according to Strasburger 

 each with its own meristem. As the layers over the tip continue 

 to divide, the outer ones become more or less separated and 

 dead, and function as a cap. The primary vascular cylinder 

 seems to be very uniformly diarch, a simpler type than prevails 

 among Dicotyledons, and much simpler than in Monocotyledons. 



II. THE SPORE-PRODUCING- MEMBERS 



THE MICEOSPOEANGIUM 



The microsporangia are always developed in connection with 

 a strobilus or strobiluslike structure, which in the genus Cycas 

 is terminal upon the main axis, and may be so in the other genera 

 of Cycadales; but it is lateral in all other Gymnosperms, and 

 either axillary or borne upon axillary spur shoots. The stro- 

 bili are almost universally monosporangiate, Tumboa giving 

 evidence of a former bisporangiate condition in the occurrence 

 of a sterile ovule in the staminate " flowers," and the Bennetti- 

 tales, in some cases at least, displaying a bisporangiate strobilus. 



In most Gymnosperms the microsporangia seem to be dis- 

 tinctly foliar, being borne by an undoubted sporophyll. In 

 some genera of Cycadales (as Cycas, Macrozamia, Ceratozamia, 

 and Stangeria) , and in Bennettitales, so far as known, the very 

 numerous sporangia, often in definite sori, and borne \ipon the 

 under surface of broad scales, are very suggestive of Filicales. 

 In other Gymnosperms, however, the sporophylls are more modi- 

 fied, and the sporangia are much fewer in number, frequently 

 being reduced to two upon each sporophyll. In certain genera 

 of Cycads (as species of Zamia) and of Conifers (as Ta.vus), the 

 peltate type of sporophyll is found, and the sporophyll of Ginkgo 

 may be regarded as a modification of it. In Conifers in general, 

 however, the expanded portion of the sporophyll develops in the 

 plane of the stalklike base. 



In Ephedra and Gnetum the microsporangia seem to be dis- 

 tinctly cauline, and are developed near the apex of a short lat- 

 eral axis which bears coalescent bractlets ("perianth"); but 

 in Tumhoa there seems to be no question as to the sporophyll 



