l6 MARSILIA QUADRIFOLIA FOUR-LEAVED MARSILIA. 



is probably derived) are formed by the rolling-up of leaves, and 

 that these leaves are little more than the involucres, or perhaps 

 bud scales, which we find in ordinary flowering plants. Mor- 

 phologically, these sporocarps, with their pedicels or stalks, are 

 probably arrested rhizomes ; for as the sporocarps develop, a 

 mucilaginous cord (equivalent to a stem or rhizome) is evolved, 

 and along it numerous oblong plates (equivalent to metamor- 

 phosed leaves) which bear the spores or reproductive bodies on 

 each side of their surface. These reproductive bodies are of two 

 kinds, — the macrospores, or "larger" spores, being the analogues 

 of pistils, or ovules ; and the microspores, or " smaller " spores, 

 which correspond to the anthers, or stamens, in flowering plants. 

 The whole process of fertilization then goes on precisely the 

 same as in the plants which we distinctively call " flowering." 

 From this plant, therefore, we can learn the valuable lesson that 

 what appears to be the fruit in these lower cryptogams is really 

 only a flower bud, analogous to the buds in pha;nogamous 

 plants. The real flowers, with their separate sexual organs, 

 develop subsequently, as in phaenogams, and, morphologically 

 speaking, are little removed from hermaphrodite, or at the best 

 monoecious plants. 



In Marsilia qtiadrifolia,. the specific name quadrifolla is, of 

 course, derived from the four-cleft leaf-blade. These blades 

 float on, or are pushed above, the surface of the water in which 

 the plant grows, and have much the appearance of an Oxalis, 

 and like the Oxalis, close their divisions at nightfall. In O.valis, 

 we have noted that very bright light acts like the absence of 

 lio;ht in causino: the leaflets to close, and it may be the same 

 with this plant. 



The specimen from which our drawing was made grev/ at 

 Cambridge, and Ave are indebted for it to the kindness of Mr. 

 Jackson Dawson, of the Arnold Arboretum, Boston. 



ExPLANATiox OF THE Tlate. — I. Sporoc.irps, with their pedicel pushing from ncr.r the 

 ba:;e of a leaf-st:ilk. — 2. Kliizome .is it creeps over the mud. — 3. Tetiole, with blade, 

 forming a perfect leaf ur frond. 



