SECT. 1 



CRYPTOGAMS 



459 



in the course of its development it supplants all the other sporogenous cells, and 

 finally the sporangial wall itself becomes flattened against the inner wall of the 

 sporocarp, frequently undergoing at the same time partial dissolution. The 

 macrospore is enveloped by a spongy perinium whose outer surface exhibits 

 numerous depressions and protuberances prolonged into filaments. At the apex of 

 the spore the perinium expands into three pear-shaped appendages. The massulae 

 become attached to the perinium. The wall of the sporocarp is ruptured at its 

 lower portion, the apical portion remaining attached to the spore in the form of 

 an ampulla-like covering. The formation of the prothallia is effected in essentially 

 the same way as in Salvinia, except that only one antheridium with eight spermato- 

 zoids arises on each of the small male prothallia protruding from a massula. 



The sporocarps of the Marsiliaceae have a more complicated structure : those of 

 Pilularia glohulifera are divided into four chambers, each with a single sorus ; in 

 Marsilia they enclose numerous sori (14-18) disposed in two rows. The sori in 

 both genera contain both micro- and macrosporangia. These arise as in all other 

 forms from superficial cells and come to lie in cavities by the upgrowth of the 

 surrounding tissue. 



In the case of the Marsiliaceae the prothallia are even more reduced than tliose 



of the Salviniaceae, but otherwise their mode of development is very similar. Each 



of the minute female prothallia formed at the apices of the macrospores produces 



a single archegonium. An apogamous 



formation of the embryo has been shown st 



to occur in a number of Australian species / 



of Marsilia belonging to the group 



Drummondii (^^''J. 



' hjij 



Class II i^s, . j _ - / x ^ _^ vl 



Equisetinae (Horse-tails) (^'^^) 



Tlie Equisetinae include only the one 

 genus Equisctum, comprising 20 species, 

 found widely distributed over the whole 

 world. Developed partly as land, partly 

 as swamp plants, they may always be dis- 

 tinguished by the characteristic structure 

 and habit of the asexual generation. They 

 have a branching, underground rhizome 

 on which arise erect, aerial haulms, usually 

 of annual growth. The rliizome of the 

 conmion Horse-tail, Equisctum arvense, 

 develops also short tuber-like branches 

 which serve as reservoirs of reserve 



Fig. 407. — Equisctum nrreuM'. Transversp sec- 

 tion through the stem, m, Lysigeiiic medul- 

 lary cavity ; (', endodermis ; cl, carinal caiials 

 ill the collateral bundles ; rl, vallecular 

 cavities ; hp, sclererichyraatoiis strands in 

 the furrows and ridges ; ch, tissue of the 

 primary cortex containing chlorophyll ; s^, 

 rows of slomata. (x 11.) 



material and hibernating organs (Fig. 408). 



The aerial haulms remain either simple, or they give rise to branch wliorls, and 

 these in turn to whorls of a higher order. All the axes are formed of elongated 

 internodes ; they have a central pith-cavity and a peripheral series of smaller air 

 channels. The collateral vascular bundles form a single circle, as seen in transverse 

 section (Fig. 407). 



At each node is borne a whorl of scale-leaves 2'ointed at the tips, and united 

 below into a sheath closely enveloping the base of the internode. The lateral 



