LICHEN HYPHAE 47 



a few spores were abstracted from the culture and examined microscopically. 

 Tulasne observed that the spore did not increase or change in volume in the 

 process of germination, but that gradually the contents passed out into the 

 growing hyphae, till finally a thin membrane only was left and still persisted 

 after two months (Fig. 14). For a considerable time there was no septation; 

 at length cross-divisions were formed, at first close to the spore, and then 

 later in the branches. The hyphae meanwhile increased in dimension, the 

 cells becoming rounder and somewhat wider, though always more slender 

 than the spore which had given rise to them. In time a felted tissue was 

 formed with here and there certain cells, filled with green colouring matter, 

 similar to the gonidia of the lichen and thus the early stages at least of a 

 new thallus were observed. The green cells, we now know, must have gained 

 entrance to the culture from the air, or they may have been introduced with 

 the water. 



B. DEVELOPMENT OF LICHENOID HYPHAE 



Lichen hyphae are usually thick-walled, thus differing from those of fungi 

 generally, in which the membranes, as a rule, remain comparatively thin. 

 This character was adduced by the so-called "autonomous" school as a proof 

 of the fundamental distinction between the hyphal elements of the two 

 groups of plants. It can, however, easily be observed that, in the early 

 stages of germination, the lichen hyphae, as they issue from the spore, are 

 thin-walled and exactly comparable with those of fungi. Growth is apical, 

 and septation and branching arise exactly as in fungi, and, in certain circum- 

 stances, anastomosis takes place between converging filaments. But if algae 

 are present in the culture the peculiar lichen characteristics very soon 

 appear. 



Bonnier 1 , who made a large series of synthetic cultures, distinguishes 

 three types of growth in lichenoid hyphae (Fig. 15): 



1. Clasping filaments, repeatedly branched, which attach and surround 

 the algae. 



2. Filaments with rather short swollen cells which ultimately form the 

 hyphal tissues of cortex and medulla. 



3. Searching filaments which elongate towards the periphery and go to 

 the encounter of new algae. 



In five days after germination of the spores, the clasping hyphae had 

 laid hold of the algae which meanwhile had increased by division; the 

 swollen cells had begun to branch out and ten days later a differentiation 

 of tissue was already apparent. The searching filaments had increased in 

 number and length, and anastomosis between them had taken place- when 



1 Bonnier 18892. 



