990 RECORD OF CURRENT RESEARCHES RELATING TO 



Atrichum undulatum ; it generally consists of three or four layers 

 of cells. 



4. This cortical tissue has nothing in common with that of Sphag- 

 num except its appearance and its physiological function ; regarded 

 from the point of development, it is entirely diflferent. It is interior 

 with respect to the epidermal layers, instead of exterior, as in the 

 Sphagnacefe. 



5. The true epidermis, characterized by the presence of hairs, 

 exists with certainty only in the lowest and subterranean portion of 

 the axis. The absolutely glabrous aerial stem is probably destitute 

 of an epidermis properly so-called ; the zone distinguished under this 

 name by authors belongs in its origin to the fundamental tissue, from 

 which it differs in its narrow coloured cells. If the true epidermis 

 is continued upwards as far as the stolons, it is only on the dorsal 

 side of the scaly appendages, following two projecting lines bordering 

 the median nerve. 



6. The multiplicity of bundles noticed by Sachs in PolytricJium 

 commune is to be observed only at the summit of the stems, and is not 

 peculiar to this species. These isolated bundles in the midst of the 

 fundamental parenchyma are not, as Sachs states, similar to the axial 

 bundle ; in addition to their never containing any medulla, they are, 

 in the Polytrichacese, more simple than this axial bundle ; while, on 

 the contrary, in Atrichum undulatum, they are remarkable for the 

 complication of their structure. 



7. A ternary symmetry prevails in the general disposition of the 

 tissues, but this is strikingly regular only in the subterranean region ; 

 in proportion to the height on the axis it becomes more obscure, and 

 finally completely disappears. 



Stomata of Marchantiacese.* — The stomata of Marchantiaceje 

 are, according to Leitgeb, of two kinds, simple and canaliculate. The 

 former, which occur in Sariteria, Grimaldia, Behoulia, Fegatella, and 

 Targionia, are epidermal pores, situated immediately above the air- 

 cavities. The latter kind, found in Marchantia and Preissia, appear 

 like canals excavated in the surface of the thallus, and opening into 

 the air-ca*vities ; they occur also in the fructification of all Marchan- 

 tiacea3. 



The mode of formation of the canaliculate stomata resembles that 

 of the intercellular spaces in the Eicciea^. On the cells which con- 

 stitute the epidermal layer at the point of the surface which lies 

 immediately behind the apex, pit-like depressions are formed at the 

 angles of the cells, which subsequently assume the appearance of 

 canals penetrating the superficial layer of cells. From this layer 

 proceeds the whole of the dorsal tissue of the thallus, which is 

 penetrated by air-cavities, including the epidermis, and the mode of 

 growth of this portion of the thallus determines whether the canals 

 retain their original form or increase to large air-chambers, which 

 tlieu either remain open through their entire breadth or are covered 

 by a growth which advances jxtri passu with their development. 

 The pits are properly to be regarded as depressions of the surface, 



* ' SB. k. Akad. Wiss. Wieu,' Jxxxi. (ISSO) p. 40. 



