328 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA. 



ferentiation is seen to be carried to a still greater extent in Meso- 

 gloia (Fig. 113) ; a plant which may be considered as one of the 

 connecting links between such Protophytes as Batrachospermese 

 — which it resembles in general plan of structure, — and the 

 Fucoid Algae, which it resembles in fructification. 



204. When we pass to the higher Sea-weeds, such as the com- 

 mon Fucus and Laminaria, we observe a certain foreshadowing 

 of the distinction between root, stem, and leaf; but this distinc- 

 tion is but very imperfectly carried out, the root-like and stem-like 

 portions serving for little else than the mechanical attachment 

 of the leaf-like part of the plant, and each still absorbing and 

 assimilating its own nutriment, so that no transmission of fluid 

 takes place from one portion of the fabric to another. Hence 

 we find that there is not yet any departure from the simple cellvr 

 lar type of structure ; the only modification being, that the 

 several layers of cells, where many exist, are of ditferent sizes 

 and shapes, the texture being usually closer on the exterior and 

 looser within ; and that the texture of the stem and roots is denser 

 than that of the expanded fronds. This simple cellular type of 

 structure is maintained through all but the highest Cryptogamia ; 

 for it is not until we come to the Mosses, that the differentiation 

 of stem, root, and leaf is established ; and even in these it is not 

 BO fully carried out, as to require a provision for the free trans- 

 mission of fluid from one part to another ; whilst the scale of 

 their fabrics is not such as to render it necessary that their softer 

 parts should be supported by a tissue of peculiar density. But 

 in the group of Ferns, which, notwithstanding their complete 

 adhesion to the Cryptogamic type of Beproduction, have the 

 general form of the higher plants, and even attain the size 

 and bearing of trees, we find the leaves separated from the roots 

 by the intervention of a stem ; and in this stem, as also in the 

 leaf-stalks prolonged from it, we find, interposed in the midst of 

 the cellular tissue which forms their principal substance, two 

 new forms of structure, — namely, woody fibre which serves to 

 give strength and support to the stem and to the organs it bears, 

 and ducts through which the liquid absorbed by the roots may 

 be readily conveyed to the leaves. 



205. The group of Melanospermous or olive-green Sea-weeds, 

 which, in the family Fucacece, exhibits the highest type of Algal 

 structure, presents us with the lowest in the family Ectocarpacex; 

 which, notwithstanding, contains some of the most elegant and 

 delicate structures that are anywhere to be found in the group, 

 the full beauty of which can only be discerned by the micro- 

 scope. Such is the case, for example, with the Sphacelaria, a 

 small and delicate sea-weed, which is very commonly found 

 parasitic upon larger Algse, either near low-water mark, or alto- 

 gether submerged ; its general form being remarkably cbarac- 

 terized by a symmetry that extends also to the individual 

 branches (Fig. 114), the ends of which, however, have a decayed 



