HIGHER CRYPTOGAIRIA AND PHANEROGAMIA.
54. In the attempt which we have made in the preceding sections to discover the order of succession in which nature has arTanged the various families included among the Algm, Fungi, and Lichens, we have en countered difficulties at every step. The extension of the same inquiry to the higher Cryptogamia and Phanerogarnia is much more satisfactory in its results. " The comparison of the history of the development of the leafy Mosses and Hepatic on the one hand, and of the Equisetacew, Rhizocarpem, and Lycopodiacem on the other," says Hofmeister, " has shown the most complete correspondence of the formation of the fruit of the one with the formation of the embryo of the other. The arebegoniunz of the Mosses, the organ within which the rudiment of the fruit (Fruchtanlage) is formed, has a structure altogether similar to that of the archegonium of the Ferns (in the widest sense)— to that part of the prothallium in whose interior the embryo of the frond-bearing plant originates. In both of these large groups of the higher Cryptogamia, we have a single cell, originating freely within the larger central cell of the archegonium, by the constantly repeated divi sions of which, in the Mosses, the fruit—in the Ferns, the leafy plant, takes its origin. In both cases the division of this cell fails to take place, and the archegonium aborts, if the spermatic filaments (Saamenf&len) do not reach it at the moment that its summit gives way." * 55. The higher Cryptogronia and Phanero gamia form a series, which, commencing with the frondose or membranous Hepaticm, ascends through the Jungermannim and Marchantive to the true Mosses. At this point, the thread is interrupted, but is easily resumed, and fol lowed through the Ferns and Lycopodiacew to the Rhizocarpem. Between these last and the Phanerogamix, there is again an interval of obscurity, which is succeeded in the latter by a new order of phenomena. The plants belonging to the series before us are charac terised by their displaying a regular alternation of two generations which differ widely in their organisation. Of these, the first, taking its origin from the germinating spore, develops two kinds of organs, the reproductive func tions of which are complementary to each other. One of these (arch egonium ) is destined
for the reception of a germ-cell, while the other (antheridium) sets free a number of cor puscles closely resembling the antherozoids of Chara, which have been already described. It is from this germ-cell that the second gene ration commences its existence ; its develop ment being, as there is now every reason to believe, dependent on the actual contact of the antherozoids. It differs completely in forrn and structure from its parent, and pos sesses only one kind of reproductive organ. This organ throws off germs (spores), each of which is capable, independently of any ex ternal influences, except those of heat and moisture of transforming itself into a new individual. This in its turn produces pistillidia and antberidia, and thus forms the starting point of a new development.
56. Supposing the history of the develop ment of the plants under consideration to com mence with the germination of the spore, and terminate with its arrival at maturity, it may be divided into two periods. Of these the first is completed in the full development of the archegonia and pistillidia, and the com bination of their products, so as to form an embryo ; while the second terminates in the full development and distribution of the spores.
57. Among the lower Hepaticae, the vegeta tive system (frond) consists of a simple mem branous expansion, which may be considered equivalent to what would result from the soldering or fusing together of the leaves and stem of a more highly developed plant. The frond is of various forms—always originally linear, and lengthens at one (the anterior) extremity only. At the other end, which is earliest formed, cessation of vegetation, and marcescence are constantly taking place. The adult plant assumes very various forms, which arise from the repeated bifurcation of the original riband-shaped shoot. In the plant, the development of which we are about to describe (Anthoceros lmvis) as one of the most simple of the Hepaticm in its structures, the fully-formed frond Is a lobed expansion of succulent, dark-green parenchyma, the general contour of which is circular. We shall divide the history of its development into two periods, corresponding with those laid down in the last paragraph.