SELAGINELLA. 357 



502. L. S. of Cone. Cut radial longitudinal sections 

 through a cone, and note 



(a) The structure of the axis, resembling that of the 

 stem, with a bundle running out to each sporophyll. 



(fe) The division of each sporophyll into a horizontal 

 lower portion, with a short downwardly -directed flap at the 

 end and a much longer upwardly -directed portion the 

 sporophyll is therefore somewhat peltate, and in some other 

 species of Lycopodium the downward portion of the expan- 

 sion or lamina is much larger than in our type. 



(c) The sporangium, inserted by a short stalk on the 

 horizontal basal part of the sporophyll, above the vein the 

 sporangium is nearly circular in section, but into the cavity 

 there projects upwards a rounded pad of tissue, making 

 the cavity kidney -shaped in outline. 



(d) The sporangium wall, consisting of an outer layer 

 of large cells and one or two inner layers of small cells 

 (disorganised in ripe sporangium) atone point on the top 

 of the sporangium but towards the outer side, the cells are 

 narrower, marking the line of dehisce nee. 



503. Structure of Sporangium Wall. In surface view, the 

 cells of the mature but not yet ruptured sporangium -wall are seen 

 to be elongated and to have thickened lignified wavy radial walls, 

 but along the dehiscence-line the cells are nearly cubical, with 

 straight radial walls ; the two rows of cubical cells have their 

 tangential as well as their radial walls lignified, as may be seen on 

 treating the preparation with aniline sulphate or with phloroglucin. 



504. Spores. Examine the spores with the high power ; they 

 are very small, roundish tetrahedral in form, and covered with 

 a network of minute projections the latter cause the spores to be 

 unwettable by water, owing to the entangled layer of air covering 

 them. 



SELAGINELLA. 



505. Nearly all the species of Selaginella are tropical, 

 mostly growing in wet forests and including epiphytes 

 and climbers, but a few are xerophytes. The simplest 

 type is that seen in the single and rare British species, 



