SELAGINELLJ8. 



385 



Four genera belong to this order, viz. , Lycopodium, which is common 

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

 Florida ; Tmesipteris and Phylloglossum, of Australia. The species 

 number from sixty to seventy, of which about fifty belong to the genus 

 Lycopodium. 



The 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 the Devonian by species of Arctopo- 

 dium. In the Carboniferous the genus Lycopodium first appeared. 



The closely related extinct order Lepidodendreae first appeared in the 

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

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

 more species, many of gi- 

 gantic size, and the order 

 by many other genera e.g., 

 Lepidophloios, Lepidostro- 

 bus, Halonia, etc. In the 

 Permian this order became 

 extinct. 



Another order the Sigil- 

 larieae waa represented by 

 many species of Sigillaria 



in the Carboniferous period. 



, . Fig. 277 /., two young plants of Selagmelln 



Like the preceding, this or- JUar-tthxii growing from the same spore ; at the 



, - - 



inrt in the top of the spore may be seen the projecting pro- 



16 thallium, ;>. //., a young plant drawn out of the 

 spore, showing the foot, f, on the left below, and 



o-iTi >11> the y UI1 root . r < on the ri2llt - m - a y un g 



gmellee. plant whwe , irst lwlve8 (co tyledons) have been re- 



The prothallia are dioecious, moved, leaving only their stipules s; between the 



m, , . , , , - latter is seen the dichotonKHuly mvl&atgpwnctum 



Those which develop from ve g et aUords; p, the protlmlliiiin Isolated from the 



Permian. 

 Oi-rior 



Order 



the macroepores consist of a spore. /. x 



protl 

 //. x 3; ///. X 30. After Hoi- 



concavo-convex many-celled 

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

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

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

 deeply sunken archegonia (Fig. 276, 1, 2, 3). The microspores develop 

 only the smallest rudiments of prothallia. In germination a single 

 cell (v, Fig. 276, 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. 276, A), and from these great numbers of 

 sperm-cells are produced (Fig. 276, 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. 276, 1), while the lower develops into the 

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



