CHAPTER XXIV. 



SPORE-PRODUCING MEMBERS OF THE LYCOPODIALES. 



THE normal sporangia in the Lycopodiales are always non-septate sacs, 



excepting that in the megasporangia of Isoetes there may be an isolation of 



the megaspore-mother-cells (see p. 320). The form is that of a kidney, of 



which the curvature and proportions are liable to considerable variation. 



The position is, as we have 



seen, essentially constant, each 



sporangium being subtended by, 



or inserted in a median position 



relatively to its sporophyll ; the 



curvature is in the tangential plane, 



showing in tangential section a 



more or less pronounced fan-like 



outline. A series of examples 



of sporangia will be selected as 



illustrating the structure and 



mode of development, and the 



degree of variation in form and 



proportion which exists within 



the phylum. 



The genus Lycopodium will 

 be taken first, and the spor- 

 angia compared in a number 

 of species. It will become 



apparent from this comparison that the differences which they show are 

 not at haphazard, but that they follow with some degree of accuracy those 

 lines of external differentiation, upon which the systematic arrangement of 

 the genus has been based. In order to make this clear the description will 

 follow the accepted systematic order, beginning with the least differentiated 

 types. In L. Selago * the sporangium originates at the base of the sporophyll, 



1 Studies, i., p. 511. 





Fui. 156. 



Radial sections through young sporangia of Lycopaditnn 

 Selago. In the youngest the whole sporophyll is shown (<?), 

 and the axis (st), and it is seen that the sporangium arises 

 upon the surface of the sporophyll. The older stages show 

 the segmentation of the sporangium. X2OO. 



