TISSUES OF mUSCINE^, ETC. 



^51 



mental tissue. Corresponding to the dorsi-ventral structure spoken of, the under side 

 dispenses with stomata : these however are so much the more numerous on the 

 upper side, and are developed in a form deviating from that usual elsewhere, as 

 is shown in Fig. 161 sp. The predominating parenchymatous fundamental tissue of 

 the Marchantia shoot is also differentiated in accordance with its ventral and dorsal 

 side. It consists of a large-celled parenchyma, in which, according to Goebel, . 

 there are forms of cells which may be looked upon at any rate as feeble indications 

 of vascular bundles; beneath the epidermis of the upper side of the shoot lies 

 a spongy assimilating tissue, which is divided up into sharply bounded areolae, each 

 opening on to the exterior through a stoma. 



From these highly organised true Mosses and Liverworts, where the most 

 essential relations of the typical systems of tissue are still to be recognised, a series 

 of forms lead by imperceptible stages down to the simplest representatives of these 

 two classes of plants, in the histological structure of which scarcely any traces of 

 differentiation are to be found. 



FIG. 160.— The mouth of the cap- 

 sule (-6) oiFoniinaLisaiUipyretica (X50). 

 ap outer, and i inner peristome (after 

 Schimper). 



FIG. 161.— Transverse section of the flattened shoot xit Marchantia poly- 

 morpha. u epidermis of lower surface; o that of the upper surface; sp 

 stoma ; chl chlorophyll tissue within an areola (bounded by ss) ; p coburless 

 parenchyma. 



I have already, in the introduction to the systems of tissue, mentioned by the 

 way that in the Algae and Fungi, when they consist of solid masses of tissue 

 (which is, of course, a necessary condition), a differentiation into epidermal and 

 fundamental tissue takes place, in which - not rarely there runs a rudimentary 

 vascular bundle consisting of long cells; and here the additional remark suffices, 

 that stomata are always wanting to the epidermal tissue, even when it is otherwise 

 sharply marked off. 



In the consideration of the external segmentation of the Algae and Fungi, it 

 was necessary to allude to the fact that instances of organisation occur, which often 

 depart so completely from the typical relations of the Mosses and vascular plants, that 

 we must look upon them no longer as rudimentary forms of the latter, but as quite 

 peculiar. The same holds also with reference to the differentiation of tissue of many 

 Algae and Fungi. Here, again, it must however suffice to illustrate by a few 

 examples what has been said ; and indeed it is chiefly a matter of establishing 

 the fact that even when the histological relations are entirely abnormal, the 



