442 



Cavers : Notes on Yorkshire Bryophytes. 



cross-sections, the thin wing is seen to arise on either side as an 

 expansion of the uppermost layers of cells of the midrib. The 

 g-reater part of the wing- consists of a single layer of cells, but 

 where it joins the midrib it is usually several (2-4) cells thick. 

 All the cells of the wing contain abundant chlorophyll grains. 

 The same is the case with the upper epidermis of the midrib ; 

 chlorophyll is present in smaller quantity in the two or three 

 layers immediately below this, but the greater part of the midrib 

 consists of colourless tissue. The cells towards the upper sur- 

 face of the midrib contain numerous starch-grains, whilst those 

 nearest the lower surface are usually traversed by fungal hyphfe, 



Fig I. —I. Transverse section tlirougli base of plant. II. Similar section taken 

 further forwarils. St., conducting strands of midrib; M., mycorhizal zone; 

 R.H., rhizoids : Lam., lamin.i or wing of thallus ; Mid., midrib. X 25. 



forming a well-developed mycorhizal zone (Fig. i). Many of 

 the cells of the ventral superficial layer grow out as long thin- 

 walled colourless rhizoids, often containing fungal hyphce which 

 pass upwards into the compact tissue of the midrib. 



The most interesting feature in the structure of the thallus is 

 the presence in the midrib of two lateral strands, the function of 

 which is that of conducting water, and which may be regarded 

 as corresponding with the more highly differentiated strands 

 found in other species of Pallavicinia (e.g., P. Lycllii). In an 

 interesting paper published recently, Mr. Tansley- remarks: 'In 

 specimens (of P. hibeniicd) from Hooker's type from Lough- 



■■'Tanslev, A. G., and Chick, Miss E., ' Notes on the Conducting- Tissue- 

 system in Bryophyta,' Annals of Botany, Vol. 15, 1901, p. 7. 



Naturalist, 



