CLASSIFICATION OF THE PTERIDOPHYTES. 125 



The spores (D) are destitute of chlorophyll and have upon the outside 

 a network of ridges, except on one side where three straight lines con- 

 verge, the spore being slightly flattened between them. 



Almost nothing is known of the prothallia of our native species. 



The second order (Ligulatce) is represented by two very 

 distinct families : the smaller club mosses (Selaginellece) and 



FIG. 74. A, one of the smaller club mosses (Selaginella) . sp. spore-bearing 

 branch, x 2. B, part of a stem, sending down naked rooting branches (r), 

 x 1. C, longitudinal section of a spike, with a single macrosporangium 

 at the base; the others, microsporangia, x 3. D, a scale and microspo- 

 rangium, x 5. E, young microsporangium, x 150. The shaded cells are the 

 spore mother cells. F, a young macrospore, x 150. G, section of the stem, 

 x 50. H, a single fibre-vascular bundle, x 150. /, vertical section of the 

 female prothallium of Selaginella, x 50. ar. archegonium. J, section of an 

 open archegonium, x 300. o, the egg cell. K, microspore, with the contained 

 male prothallium, x 300. x, vegetative cell. sp. sperm cells. L, young 

 plant, with the attached macrospore, x 6. r, the first root. I, the first leaves. 



the quill-worts (Isoetece). Of the former the majority are 

 tropical, but are common in greenhouses where they are prized 

 for their delicate moss-like foliage (Fig. 74, A) . 



