SELAQINELLJE. 



385 



Four genera belong to tbis order, viz. , Lycopodium, wliich is common 

 in the wooded portions of tlie United States ; Psilotum, found in 

 Florida ; Tmesipteris and Phylloglossum, of Australia. Tbe species 

 number from 115 to 130, of whicli about 100 belong to tbe genus 



Tbe spores of Lycopodium clavatum are gathered in Europe and 

 sold for various minor uses. Many species have a high ornamental 

 value. 



This order was represented in tbe Devonian by species of Arctopo- 

 dium. In the Carboniferous tbe genus I/yeopodium first appeared. 



The closely related extinct order Lepidodendrese first appeared in the 

 Devonian, in which it was represented by two known species of Lepi- 

 dodendron ; in tbe Carboniferous this genus was represented by sixty or 

 more species, many of gi- 

 gantic size, and the order 

 by many other genera — e.g., 

 Le-pidophloios, Lepidostro- 

 bus, Halonia, etc. In the 

 Permian tliis order became 

 extinct. 



Another order — tbe Sigil- 

 larjeae — was represented by 

 many species of Sigillaria 

 in the Carboniferous period. 

 Like the preceding, this or- 

 der became extinct in the 

 Permian. 



Order Selaginellce. — 

 Tbe prothallia aredioecious. 

 Those which develop from 



the macrospores consist of a spore. /. X 5 ; II. x 3; 



■^ ,, , meiBter. 



concavo-convex many-celled. 



structure, which develops upon, and has its concave side applied to, tbe 

 convex surface of tbe spore. Upon its convex surface, which protrudes 

 through the ruptured wall of the spore, are a few root-hairs and many 

 deeply sunken arcliegonia (Fig 276, 1, 3, 3). The microspores develop 

 only tbe smallest rudiments of prothallia. In germination a single 

 cell (», Fig. 376, D) is first of all cut off ; this undergoes no further 

 change, and is doubtless to be regarded as the prothallium. The re- 

 mainder of the spore becomes divided in a regular way into a few 

 large primordial cells (Fig. 376, A), and from these great numbers of 

 sperm-cells are produced (Fig. 376, D). 



After fertilization the germ-cell divides at right angles to the axis 

 of the archegonium (Fig. 276, 3) ; from the upper cell so formed a 

 suspensor is developed (Fig. 376, 1), while the lower develops into tbe 

 embryo. The embryo, by its rapid growth, comes eventually to occupy 



Fig. 277. — /., two young -plants of SelagineUa 

 Martensii growing from the same spore ; at the 

 top of the spore may he seen the projecting pro- 

 thallium, p. 11.^ a young plaut drawn out of the 

 spore, showing the foot, /", on the left below, and 

 the young root, r, on the right. 7//., a young 

 plant whose first leaves (cotyledons) have been re- 

 moved, leaving only their stlpulesj «,* between the 

 latter is seen the dichotomously dividing^ww-c^m 

 ' " ' /), the prothallium isolated from the 

 - " — ///. X 30.— After Hoi- 



