52 FIBRO-CELLULAR TISSUE. [BOOK i. 



Fegatella conica consists almost entirely of cells the partitions 

 of which are either distinctly porous or thickened beautifully 

 with network. 



" Among mosses, Dicranum Schraderi, spurium, &c., are 

 distinguished by having the cells of the leaves very thick- 

 sided, and pierced by wide or funnel-shaped pore canals. 

 Still more conspicuously do these spiral and porous formations 

 display themselves not only in Sphagnum, but in the whole 

 group of Leucophanese. The structure of the cells of 

 Sphagnum, Leucobryum vulgare (Dicranum glaucum) and 

 Octoblepharum albidum has been pointed out by Mohl. The 

 great pores, which in the older state of the leaf become real 

 holes, also occur in Octoblepharum cylindricum, Didymodoii 

 sphagnoides, and in Leucobryum minus, albidum, and 

 longifolium. In fact, all the mosses called Leucophanese are 

 characterised, like Sphagnese, by peculiarities in the structure 

 of the leaf, which consists of two different species of cells, 

 some narrow and filled with chlorophyll, others wider, trans- 

 parent, and perforated with pores, which afterwards pass into 

 holes." (See Annals of Natural History, vol. v. p. 73.) 



It may, however, happen that a spiral appearance is given to 

 cellular tissue, without the actual presence of any spiral 

 structure, of which an example is given by Dr. Willshire. 



In the twisted seed-vessel of Loasa lateritia, he found that 

 the cellular tissue consisted of long cells, " closely approaching 

 to, or even apparently identical with, one portion of the 

 woody tissue of the stem, and marked longitudinally by a 

 single row of dots or pores exactly like those on the ducts of 

 the vascular system of the plant : the fibres of the different 

 layers crossed each other obliquely, so that when two layers 

 are examined under the microscope the structure is netted, 

 and between each mesh a single pore is seen." (Annals of 

 Natural History, vol. x. p. 5.) 



The principal varieties are these : 



A. Membrane and Fibre combined. 



1. Fibres twisted spirally, adhering to a spheroidal or angular 

 membrane, and often anastomosing irregularly, without 

 the spires touching each other. (Plate I. fig. 12.) This 



