228 



PTERIDOPHYTA. 



Highlands of Scotland. The other genus of the order is Phylloglossum, with 

 one species, P. drummondi (Australia, Tasmania, and New Zealand), a small 

 plant only a few centimetres high, with two tubers, and about eleven linear 

 leaves at the base of the stem which is terminated by a cone of sporophylls. 

 FOSSIL Lycopodiaceas in the Carboniferous period. 



OFFICINAL: "Lycopodium," the spores of L. clavatum. 



Family 2. Psilotaceae. The sporangia are placed on the apex of short, two- 

 leaved stems, as 2-3, seldom four, small capsules. Small herbs, with angular 

 stems; leaves small, simple, and one nerved. Only four species. Psiloium 

 (Madagascar, Moluccas, Sandwich Islands, etc.) is destitute of roots, their place 

 being supplied by special underground stems which bear a few modified leaves, 

 very much reduced, especially when buried deeply in the soil. Three species. 

 Tmesipteris (Australia), one species. 



Sub-Class 2. Selaginelleae (HETEROSPOROUS Lycopodinse). 

 Micro- and macro-spores. The prothallia are very much reduced, 



especially the male; the female does not leave the spore. 

 leaves are ligulate. 



The 



A D C 



FIG. 233. Germination of the microspores of Sclfaginclla : A the spore rendered 

 transparent, seen from above. In the iutci'ior is seen the prothallinm (/), and the first 

 divisions of the antheridium (a, b, c, d) , in B the spore- wall is removed and all 

 the spermatozoid-mother-cells formed; in C, the microspore has opened and the spermato- 

 zoids and the mother-cells are escnping togetl, er. 



The sexual generation. In the MICROSPORES are formed: 

 (1) a very small " vegetative " cell (/ in Fig. 223 A, B), and (2) 

 a cell many times larger (the antheridium) which divides into a 

 number (4-8) of peripheral cells, enclosing 2-4 inner cells, which 

 last form a large number of spermatozoid-mother-cells in 

 Selaginetta but only 4 in Isoetes. On germination, when the 

 spore- wall is ruptured, the spermatozoids and spermatozoid-mother- 

 cells are ejected into the water. 



The SPERMATOZOIDS in Selaginella are elongated and club-shaped, 

 with two cilia (Fig. 234) ; but in Isoetes lacustris they are spirally- 

 twisted threads which differ from all other spermatozoids by 



