MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA. 335 



was until recently known to exist in this group, is the production and 

 liberation of i tetraspores ' (Fig. 213, B), formed by the binary subdivision 

 of the endochromes of special cells, which sometimes form part of the 

 general substance of the frond, but sometimes congregate in particular 

 parts, or are restricted to special branches. If the second binary division 

 takes place in the same direction as the first, the spores forming the 

 tetraspore are arranged in linear series; but if its direction is trans- 

 verse to that of the first, the four spores cluster together. These, 

 when separated by the rupture of their envelope, do not comport 

 themselves as t zoospores/ but, being destitute of propulsive organs, are 

 passively dispersed by the motion of the sea itself. Their production, 

 however, taking place by simple cell-division, and not being the 

 result of any form of sexual conjunction, the 'tetraspores' of the 

 Rhodospermece must be regarded, like the zoospores of the Ulvaceca, 

 as gonidia, analogous rather to the buds than to the seeds of 

 higher Plants. It is now known that a true Generative process takes 

 place in this group, but the sexual organs are not usually found on the 

 plants which produce tetraspores; so that there would appear to be an 

 alternation between the two modes of propagation. Antheridial cell are 

 found, sometimes on the general surface of the frond, more commonly at 

 the ends of branches, and occasionally in special conceptacles. Their 

 contents, however, are not motile i antherozoids/ but minute rounded 

 particles having no power of spontaneous movement. Sometimes on the 

 same individuals as the antheridia, and sometimes on different ones, are 

 organs that curiously prefigure the pistil in flowering plants; each con- 

 sisting of a projecting cluster of cells, from which arises a long cell-tube 

 termed the trichogyne. Fertilization is effected by the attachment of 

 one of the antheridial particles to the trichogyne, the walls of which are 

 absorbed at that spot, so that the fertilizing material passes down its tube 

 to the cluster of cells at its base; and ( oospores' are thus formed either 

 among these or in adjacent cells. In the true Corallines, which are Rhodo- 

 sperms whose tissue is consolidated by calcareous deposit, the tetraspores 

 are developed within a ceramidium, 

 which is an urn-shaped case, furnished 

 with a pore at its summit, and contain- 

 ing a tuft of pear-shaped spores arising 

 from the base of its cavity. 



331. Hepaticce. Quitting now the 

 Algal type, and entering the series of 

 Terrestrial Cryptogams, we have first 

 to notice the little group of Hepaticce or 

 Liverworts, which is intermediate be- 

 tween Lichens and ordinary Mosses;- 

 agreeing rather with the Algal thallus 

 of the former in its general mode of 

 growth, whilst approaching the latter 

 in its fructification This group presents 

 numerous objects of great interest to the 

 Microscopist; and no species is richer in these than the very common 

 Marchantia Polymorpha, which may often be found growing between 

 the paving stones of damp court-yards, but which particularly luxuriates 

 in the neighborhood of springs or waterfalls, where its lobed fronds are 

 found covering extensive surfaces of moist rock or soil, adhering by the 

 radical (root) filaments which arise from their lower surface. At the 

 period of fructification these fronds send up stalks; which carry at their 



