VASCULAEIA. 427 



and the microspores rudimentary male prothallia. Illustrative 

 (reiiera : tialvima, Micheli ; Marsilea, H. 



Structure and Life-history. The sexual generation of the Rhizo- 

 carpese strongly resembles that of the Selaginellaceae. Here also the 

 microspores produce the male prothallia. In Salvinia this is effected by 

 the protrusion from the microspore of tubes, each of which divide into 

 two cells at the apex, the contents of which form each four spermato- 

 zoids. In Marsilea and Pihdaria the spermatozoids are formed within 

 the microspore, thus : first eight cells are formed, and then the contents 

 of each produce four spermatozoids 32 in all. The spermatozoids escape 

 through a small funnel-like opening at one end of the microspore. 

 The female prothallia are produced by the macrospores : they remain 

 enclosed at first by the funnel at the apex of the macrospores and are 

 bounded on the underside by a diaphragm, which separates it from a 

 large intercellular space within. The funnel at the apex then opens 

 asunder, and the protliallium is almost entirely protruded by a bulging 

 motion of the diaphragm ; on it are formed the archegonia, which after 

 fertilization by the spermatozoids, give rise to the asexual spore-bearing 

 generation. 



_ Affinities, &c. This Order is closely related to the preceding one (Sela- 

 gineilaceae) in the nature of its reproduction, and to the Filices in its 

 vegetative structure. The Rhizocarpeae are aquatic or marsh plants. The 

 genus Salvinia is represented by rootless plants which are found floating 

 tree in the water of stagnant pools ; the submerged leaves are finely lacini- 

 ated and resemble roots, but their segments bear sporocarps (fig. 496 A,/). 

 The genus Marsilea with its allies, of which Pilularia is our only native 

 example, is composed of herbaceous plants, the stem of which is little 

 developed and consists of a kind of rhizome giving off tufts of filiform 

 adventitious roots on the underside and two or more series of leaves on 

 the upper. They are found growing in the mud at the margins of pools. 



Qualities and Uses, They have no known medicinal or economic pro- 

 perties, unless perhaps Marsilea salvatrix (the Nardoo of Australia), the 

 spores of which are said to have been eaten in cases of scarcity. 



Division II. Muscineae. 



Cormophytal Cryptogams possessing imperfect vascular tissue only. 



The Muscinece consist of the Mosses and Hepaticae, and resemble the 

 Vascular Cryptogams in the fact that their life-history consists of two 

 alternating generations a sexual and an asexual. When the spore borne 

 by the asexual generation germinates it produces the sexual generation. 

 This is effected, indirectly in the case of the Mosses and a few Hepaticse, 

 by the production of a protonema (a confervoid prothallium), out of which 

 the sexual generation arises, and directly in the other Hepaticse. The 

 sexual generation preponderates in the vegetative quality, and forms the 

 plant commonly known as a Moss or a Hepatic, as the asexual generation 

 does in the Vascular Cryptogams. It bears the anthendia (male organs) 

 and the archegonia (female organs). From the fertilized central em- 

 bryonic cell of the archegonium there arises the asexual generation 



