462 BOTANY rAur ii 



In certain species some of the aerial liaulms always remain sterile, branching 

 profusely, -while others which produce the terminal cones either do not branch at 

 all, or only at a later stage, and then sparingly. This distinction between the 

 sterile and fertile haulms is most marked in Equisehim arvense and Equisctum 

 Telmateja, in both of which the fertile shoots are entirely unbranched, and 

 terminate in a single cone (Fig. 408). Resembling in their mode of life a parasite 

 upon the rhizome, they are otherwise distinguished from the vegetative haulms by 

 their lack of chlorophyll and their light yellow colour. 



Equisetum gigantcum, growing in South America, is the tallest species of the 

 genus ; its branched haulms, supported by neighbouring plants, attain a height of 

 over twelve metres, and are about two cm. in diameter. 



Tlie spores are all of one kind, and on germination give rise to thalloid 

 PUOTHALLIA which are generally dioecious (Fig. 409). The female prothallia are 

 larger than the male, and, branching profusely, are prolonged into erect ruffled 

 lobes at whose base the archegonia are produced. In structure the archegonia 

 resemble those of the Ferns, but the upper cells of the four longitudinal rows of 

 cells constituting the neck are more elongated and, on opening, curve strongly 

 outwards. The first leaves of the embryo are arranged in a whorl and encircle the 

 apex of the stem. The growth of the embryo is effected by the division of a three- 

 sided apical cell (Figs. 113, 114). 



The outer epidermal walls of the stem are more or less strongly impregnated 

 with silica. In Equisetum hiemale, and to a less degree in Equisetum arvense, the 

 silicificatiou of the external walls is carried to such an extent that they are used 

 for scouring metal utensils and for polishing wood. 



Poisonous substances are formed in some species of Equisetum, and hay with 

 which the shoots are mixed is injurious to cattle. 



Class III 

 Lycopodinae (Club Mosses) 



To the Lycopodinae belong, as their most important genera, 

 Lijcopodium, SelagineUa, and Isoetes. They are distinguished from the 

 other Pteridophyta, by their general habit and the mode of their 

 sporangial development. 



The dichotomous branching of the stem (Figs. 18, 19) and root and 

 the simple form of the leaves are characteristic of the sporophyte. 

 The two first-named genera have elongated stems and small leaves ; 

 Isoetes on the other hand has a tuberous stem and long awl-shaped 

 leaves. Unlike the fertile leaves of the Filicinae and Equisetinae, 

 which always bear numerous sporangia, the sporophylls of the 

 Lycopodinae produce the s])orangia singly, at the base of the leaves 

 or in their axils. Although in many cases scarcely distinguishable 

 from the sterile leaves, the sporophylls are frequently distinctively 

 shaped, and, like those of Equisetum, aggregated at the ends of the 

 fertile .shoots into terminal spike -like cones or flowers. Compared 

 with the leaves, the sporangia are relatively large and have a firm 

 wall of a number of layers of cells. The innermost layer of the 



