and gelatinous, and is therefore known as a Gelathious 

 Liclien. Farmelia, another lichen, becomes leathery 

 when saturated witli water, and this, therefore, is 

 placed in the non-gelatinous class. Collema is again 

 classed as a Foliaceous Lichen, because its thallus is 

 green and leaf-like in appearance. 



2. STRUCTURE. 



In section Collema shows an epidermis or cortical 

 rind, forming a sort of pseudo-parenchyma. This 

 rind consists of a number of septated hyphcB, which 

 do not differ in any particular from the hyphae of the 

 fungi already discussed. It is the cut ends of these 

 elements which are seen in section. The interior 

 consists of a colorless jelly, in which lie chains of 

 gonidia and numerous hyphm. The gonidia and 

 hyphee are about equally mingled, and the thallus is 

 said to exhibit a homoiomerous structure. 



(a) Gonidia- The wall of each cell is composed of 

 normal cellulose, lying next to this is a band of 

 protoplasm containing chlorophyll grains, and the 

 centre is occupied by either a colorless or a blue 

 vacuole. A nucleus is always present embedded in 

 the protoplasm. These cells — gonidia— are arranged 

 in bead-like rows. One or more cells in each chain 

 is larger than its neighbours, and is colourless. 



(b) The Jelly is now universally believed to be the 

 outer gelatinous walls of the gonidia. 



