3°° 



PART IV, VEGETABLE TAXONOMY. 



lateral branches, and partially protected by two small leaves 

 which rise on either side of them. The sporangia are in a 



cluster of from two to four, 

 and bear but one kind of 

 spores. See Fig. 566. 



Order C. The Ligu- 

 latae. The order is so 

 named by reason of the 

 fact that the leaves possess, on 

 their upper surface near the base, 

 a membranous appendage some- 

 what resembling the ligule of 

 grasses. All the species produce 

 two kinds of spores, large female 

 macrospores and much smaller 

 male microspores borne in sepa- 

 rate sporangia. The female pro- 

 thallium is small and projects but 

 little from the coats of the spore, 

 and the male prothallium, as in 

 the heterosporus Filicinese, is still 

 further reduced, consisting of 

 only a single minute cell which 

 B A bears the antheridium. 



Fig. 566. — Psilotum triquetrum. A, part of plant, natural size. B, portion of stem, 

 magnified, showing fructifying branch bearing at its apex two sporangia between two small 

 leaves. 



There are two sub-orders, the Selaginellece and the Isoetece. 



The Selaginellas, in general appearance, bear a considerable 

 resemblance to the species of Lycopodium, but the dichotomous 

 branching is in one plane and not in all planes ; the leaves are 

 arranged in four vertical rows, and the members of opposite 

 pairs are dissimilar in size or shape ; and the roots fork repeat- 

 edly, and the secondary branches decussate with the primary, 

 the tertiary with the secondary, and so on. The sporangia are 

 borne on the stem immediately above the insertion of the leaves 

 so as to appear in their axils. The sporangia occur singly, and 

 are of large size compared with those of Ferns ; the macrospo- 

 rangia each contain four spores, while the microsporangia, 

 which are ordinarily borne higher up on the axis, contain 



