American Species of Marchantia. 217 



2. Compact Ventral Tissue 



The ventral tissue in Marchantia gradually thins out from the 

 thickened median portion until it is frequently only two or three 

 cells thick along the margins of the thallus. It consists primarily 

 or even wholly of parenchyma and its chief function apparently is 

 to act as a storage-tissue for water and organic food. In some 

 parts of the thallus it is usually possible to demonstrate the 

 presence of elongated pits in the cell-walls, and a purplish pig- 

 mentation of the walls is often apparent. Cells containing oil- 

 bodies are usually conspicuous among the other parenchyma cells 

 (Fig. 20, A) and seem to be present in all the species. In 

 herbarium material, however, it is not always easy to demonstrate 

 them. Cells containing mycorrhiza are likewise very frequent. 

 In M. chenopoda, as noted by Leitgeb and Prescher, the ventral 

 tissue and the partition walls between the air-chambers contain 

 scattered slime-cells similar to those foimd in the epidermis. 

 Slime-cells of this character occur also in the compact tissue of 

 M. paleacea, M. breviloba sp. nov. and the East Indian M. emar- 

 ginata, but have not yet been detected in other species except in 

 connection with the reproductive organs. According to Cavers^^ 

 the slime-cells and slime-canals of Conocephalum conicum fail to 

 develop when the plants are cultivated under water, and it is 

 therefore possible that slime-cells may not always be present in 

 the species of Marchantia just listed. In fact Prescher reported 

 that they were absent from M. emarginata, and specimens of M. 

 paleacea and of M. chenopoda might be cited where they are 

 very infrequent or perhaps not present at all. 



The only cells found in the ventral layer which are not 

 parenchymatous in their nature are the more or less elongated 

 sclerotic cells with yellow or brown walls, which occur in certain 

 species. Cells of this character were first demonstrated by 

 GoebeP^ in the case of Preissia quadrata (Scop.) Nees, and the 

 same author has called attention to their occurrence in the New 

 Zealand M. foliacea Mitt.^^ In this species, according to his 

 account, the sclerotic cells are variable in length and are usually 

 scattered singly among the parenchyma cells. Occasionally two 



k 



" Ann. Bot. 18 : 93.' 1904. 



^ Arb. Bot Inst. Wurzburg 2 : 533. 1882. 



" Flora 96 : 194. /. I43- 1906. 



Trans. Conn. Acad., Vol. XXI 15 iQi? 



