CELLS AND CELL PRODUCTS 



217 



slices and of dissolving away the lime enabled them to see the tissues in 

 their relative positions. In these immersed lichens, as described by them and 

 by previous writers, and more especially in calcicolous species, the gonidial 

 zone of Protococcaceous algae lies near the surface of the rock, and is 

 mingled with delicate, thin-walled hyphae which usually do not contain oil. 

 The more deeply immersed layer is formed of a weft of equally thin-walled 

 hyphae, some of the cells of which are swollen and filled with fat globules. 

 These oil-cells may occur at intervals along the hyphae or they may form 

 an almost continuous row. In addition, strands or bundles of hyphae (Fig. 

 1 1 8) containing few or many oil globules traverse the tissue, and true 



a 



Fig. 1 1 8. Biatorella (Sarcogyne) simplex Br. and Rostr. 

 a, sphaeroid oil-cells; b, strand of oil-hyphae from 

 10-15 mm. below the surface, x 585 (after Lang). 



sphaeroid cells are generally present. These latter arise in great numbers 

 on short lateral branchlets, usually near the tip of a filament and the groups 

 of cells are not unlike bunches of grapes. Sometimes the oil-cells are massed 

 together into a complex tissue. Hyphae from this layer pierce still deeper 

 into the rock and constitute the rhizoidal portion of the thallus. They also 

 produce sphaeroid oil-cells in great abundance (Fig. 1 19). In the immersed 



Fig. 1 1 9. Biatorella pruinosa Mudd. a, complex of sphaeroid 

 oil-cells from 10 mm. below the surface; b, hypha of sphaeroid 

 cells also from inner part of the thallus. x 585 (after Lang). 



