XII 



EQUISETINEJE 



475 



layer by the absorption of the others, but the remains of a sec- 

 ond layer can be made out in stained sections of the ripe sporan- 

 gium (Fig. 280, E). The vascular bundles of the sporophyll 

 divide, one branch running to each sporangium. 



Of the two species studied by Bower, E. arvense and E. li- 

 mosum, the latter showed more slender and strongly projecting 

 sporangia, but otherwise they were alike. E. tehnateia has 

 even more massive sporangia than E. arvense. The sporophylls 



FIG. 278. Longitudinal section of an older sporangium, X26o. The nuclei are shown 

 in the archesporial cells. 



form a regular cone at the apex of the fertile branch, and are 

 arranged in regular whorls, which vary in number in propor- 

 tion to the size of the cone. The top of the sporophyll is al- 

 ways polygonal in outline, owing to the lateral pressure of its 

 neighbours, and very often they are regularly hexagonal, but 

 this bears no relation to the number of sporangia, which usually 

 exceed in number the angles of the sporophyll. 



Development of the Spores 



The development of the spores in Eqmsetum, while agree- 

 ing in many respects with that of the eusporangiate Ferns, shows 

 some peculiarities that are noteworthy, and as this offers one 

 of the best cases for studying spore-formation, it was somewhat 



