444 



Cavers: Notes on Yorkshire Bryophytes. 



consists of about a dozen cells in cross-section, whilst on 

 long-itudinal section each cell is seen to be many times longer 

 than wide (Fig's. 2, 3). As a rule, these strand-cells give the 

 reactions of lignified cell-walls, becoming deep-red when treated 

 with phloroglucin, and yellow with aniline chloride, but in some 

 cases the lignin-reactions are feeble or absent. The strand-cells 

 are somewhat narrower than those of the surrounding tissue, 

 from which they stand out clearly in sections. At first sight 

 they appear to contain nothing but water, whilst the surrounding 

 cells contain abundant starch-grains or sometimes densely- 

 woven fungal hyphas. Closer examination shows that each 

 strand-cell is lined by a thin layer of protoplasm, which lies on 

 the inner surface of the cell-wall, and is especially well seen 



P'ST- 3- — Part of a longitudinal section of the midrib, traversing one ot 

 the conducting strands. On either side of the elongated hyaline strand- 

 cells are the cortical cells, packed with starch grains. X iSo. 



when the cells are plasmolysed with salt solution. In the 

 posterior portion of the midrib the strand-cells are usually 

 found to be devoid of a nucleus, but further forwards, in the 

 younger parts of the shoot, each strand-cell shows a large 

 nucleus, generally ovoid or flattened and applied to the cell-wall ; 

 apparently the nuclei at a later stage become broken up and 

 disappear. 



In stained longitudinal sections, the lateral walls of the 

 strand-cells show here and there areas of oval or rounded 

 outline, where the membrane is very thin, and sometimes, 

 especially in the bare hinder region of the midrib, actual open- 

 ings or pores are seen. The cross-walls between the strand- 

 cells are usually much thinner than the longitudinal walls, and 

 are frequently perforated, so that the cells placed end to end are 

 put in open communication. 



{To be continued.^ 



Naturalist, 



