XIII 



EQUISETINE^ 



453 



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

 second layer can be made out in stained sections of the ripe 

 sporangium (Fig. 241, E). The vascular bundles of the sporo- 

 phyll branch, one branch running to each sporangium. 



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

 liinosum, the latter showed more slender and strongly projecting 

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

 even more massive sporangia than E. arvense. The sporo- 

 phylls form a regular cone at the apex of the fertile branch, 

 and are arranged in regular whorls, which vary in number in 



Fig. 239. — Longitudinal section of an older sporangium, x 260. The nuclei are shown in the arche- 



sporial cells. 



proportion to the size of the cone. The top of the sporophyll 

 is always 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 Eqnisetiini, 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 



