All the plants considered in the preceding chapters are included in the term CRYPTOGAMS; all in the following chapters under the head of PHANEROGAMS (see page 3). Hofmeister’s pioneer works (1851, _Vergleichende Untersuchungen der höheren Kryptogamen_, etc.) and the numerous researches published later by other investigators, have closed the gap which was formerly thought to exist between these plants; so that we now, in the series: Bryophyta--Pteridophyta--Gymnospermæ--Angiospermæ see the expression of a single line of development in accordance with a definite plan. The forms through which this gradual development has taken place have in course of time, however, to a great extent died out, and only single links of the chain connecting the lowest to the highest still remain. THE ALTERNATION OF GENERATIONS, which we found indicated in certain Thallophytes, can be proved with the greatest clearness in all the higher Cryptogams, from the Mosses upwards; it is also found in the Phanerogams, but not in such a pronounced degree, because one of the generations is so far reduced that it has almost given up its independence. For the sake of greater clearness, we will begin with the comparison of the sporophyte, asexual (second) generation. =The asexual (2nd) generation of the Cormophytes.= The asexual generation which follows from the further development of the fertilised oosphere, is, in the _Mosses_, only the sporogonium (according to one theory it is perhaps homologous with a spore-bearing leaf, situated upon a short stem, see p. 187); in _Filicinæ_, _Equisetinæ_, and _Lycopodinæ_, on the other hand, it is a highly developed plant differentiated into stem, leaf, and true root, and bearing the sporangia on its leaves. The ~MODIFICATION OF THE SHOOT~ is very slight in _Filicinæ_. The first leaves of the embryo are very simple in form (Fig. 205), but after a certain age all the leaves which arise are essentially alike. The fertile leaves do not differ from the barren ones, and are found associated with them, and their formation does not limit the growth in length of the stem. It is only in a few of the true Ferns, and in the Hydropterideæ, that the fertile leaves differ considerably from the barren ones. A division of labour in which certain leaves are set apart for nutrition, and others for reproduction, is found more pronouncedly in the _Equisetinæ_ and _Lycopodinæ_, for in these groups, with a few exceptions, the fertile and barren leaves are very dissimilar; the former are collected in special ear-like _cones_, which _terminate the further growth_ of the short stems on which they are borne. In connection with the cone, leaves are sometimes developed which form a transition from the barren to the fertile ones (the “annulus” in Equisetaceæ), and in these cases the first indication of a flower with perianth or floral-leaves is to be traced. Among the Cryptogams the highest division of labour is found