217 

 CHAPTER III. 



LePRARIACEAE PSEUDOLICHENES. 



In this group I have temporarily classed those structures whose 

 position among lichens is uncertain, or which are perhaps not true 

 lichens. The principal genera occurring in the territory are 

 Le-pra and Amphiloma ; of the former we have the representative 

 L. viridis Schaer., which is common everywhere, occurring on trees, 

 fences, and rocks in moist shaded places ; it is usually recognized 

 as Pleurococcus ( Protococcus) vulgaris ; upon closer examination it is, 

 however, found that it consists of an association of Pleurococcus with 

 the hyphal network of some fungus ; the fungal portion never produces 

 apothecia ; it is also found that in some instances the hyphae are al- 

 most entirely wanting ; it is, therefore, in all probability, a case of 

 contingent symbiosis (see Contingent Symbiosis) . The structural 

 association of the hyphae with the algal cells is less intimate than in 

 true lichens (see Fig. 2, pi. 1). The haustorial branches do not 

 form such a complete covering or network about the algae ; in no 

 instance have I noticed that the haustoria penetrate the alga. In 

 some instances Lepra develops a growth which to external appear- 

 ances resembles a typical crustaceous thallus ; it differs, however, 

 in the absence of layer-differentiations ; that is, algae and hyphae 

 are about uniformly intermingled ; it differs also in the fact that its 

 limitations of growth are not so fixed as in the true lichen thallus ; 

 it may spread over areas several yards in diameter, or it may cover 

 the entire side of a large tree-trunk. 



As to the origin of the hyphae nothing definite is known at pres- 

 ent. In general it is found that they are quite uniform in the structure 

 and size of the hyphal cells ; the filaments are much contorted and 

 twisted, and the new branches are formed very nearly at right angles 

 to the mother-branch. I am unable to state whether these hyphae 

 originate from spores (of fungi or lichens) or whether they are hy- 

 phal branches derived from some lichen or fungus growing in the 

 vicinity; it is known that hyphae may grow to a great length under 

 suitable conditions. Such suitable conditions are no doubt supplied 

 by the algae which furnish the hyphae with an abundance of assimi- 

 lated food substances, thus enabling them to grow indefinitely ; 

 apothecia are not formed because of this hypernutrition. It is also 



