CRYPTOGAMS 413 



the haulms themselves assume the function of assimilation, and for 

 that purpose their cortical tissue under the epidermis is provided with 

 chlorophyll. 



The SPORANGIA are formed of specially shaped leaves or sporo- 

 phylls. Like the scale leaves the sporophylls are developed in whorls, 

 but are closely aggregated at the tips of the erect fertile shoots into 

 a cone (Fig. 347, 1, a), which is sometimes spoken of as a flower, 

 from the correspondence in its structure to the male flower of the 

 Conifers. The lowest whorl is sterile, and forms a collar-like pro- 

 tuberance, which may be regarded as a modified form of perianth. 

 The sporophylls (Fig. 347, 3, 4) are stalked and have a shield-shaped 

 lamina, on the under side of which are borne the sac-like sporangia (5- 

 10). In the young sporangium the sporogenous tissue is surrounded 

 by a wall consisting of several cell layers, but eventually the so-called 

 tapetal cells of the inner layers become disorganised, and their proto- 

 plasm penetrates between the developing spores. At maturity, the 

 wall of the sporangium consists only of the outermost of the original 

 layers whose cells are provided with annular and spiral thickenings ; 

 the sporangia thus resemble the homologous pollen-sacs of Phanero- 

 gams. The sporangia split longitudinally, and set free a large 

 number of green spores, which are nearly spherical in shape, and have 

 peculiarly constructed walls. In addition to the intine and exine, 

 the spores are overlaid with a perinium formed from the protoplasm 

 of the tapetal cells, and consisting of two intersecting spiral bands 

 which are attached to the spores only at their point of intersection 

 (Fig. 347, 5-7). On drying, the spiral bands loosen and become 

 uncoiled ; when moistened they close again around the spore. By 

 means of their hygroscopic movements they serve to hook together 

 the spores, and in this way is assured the close proximity of the 

 unisexual prothallia which they produce. 



In certain species some of the aerial haulms 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 Equisetum arvense and JEquisetum Telmateja, in 

 both of which the fertile shoots are entirely unbranched, and terminate in a single 

 cone (Fig. 347, 1). 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. 



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

 thalloid prothallia, which are generally dioecious. In the adjoining 

 figure (Fig. 348) a male prothallium of Equi&etwm arvense is represented, 

 showing the first formed antheridia (a) somewhat sunk in the tissue. 

 The female prothallia attain a large size, 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 

 (</. Fig. 339, p. 406), but the upper cells of the four longitudinal 



