LICHEN HYPHAE 49 



C. Culture of Hyphae without Gonidia ' 



Artificial cultures had demonstrated the germination of lichen spores, 

 with the formation of hyphae, and from synthetic cultures of fungus and 

 alga complete lichen plants had been produced. To Moller^ we owe the first 

 cultures of a thalline body from the fungus alone, both from spermatia and 

 from ascospores. The germination of the spermatia has a direct bearing 

 on their function as spores or as sexual organs and is described in a 

 later chapter. 



The ascospores of Lecanora subfusca were caught in a drop of water on 

 a slide as they were ejaculated from the ascus, and, on the following day, a 

 very fine germinating tube was seen to have pierced the exospore. The 

 hypha became slightly thicker, and branching began on the third day. If 

 in water alone the culture soon died off, but in a nutrient solution growth 

 slowly continued. The hyphae branched out in all directions from the spore 

 as a centre and formed an orbicular expansion which in fourteen days had 

 reached a size of •: mm. in diameter. After three weeks' growth it was large 

 enough to be visible without a lens ; the mycelial threads were more crowded, 

 and certain terminal hyphae had branched upwards in an aerial tuft, this 

 development taking place from the centre outwards. Moller marked this 

 stage as the transition from a mere protothallus to a thallus formation. In 

 three months a diameter of i"5-2 mm. was reached; a transverse section 

 gave a thickness of -86 mm. and from the under side loose hyphae branched 

 downwards and attached the thallus, when it had been transferred to a solid 

 substratum such as cork. Above these rhizoidal hyphae, a stratum of rather 

 loose mycelium represented the medulla, and, surmounting that, a cortical 

 layer in which the hyphae were very closely compacted. Delicate terminal 

 branches rose into the air over the whole surface, very similar in character 

 to hypothallic hyphae at the margin of the thallus. 



Lecanora subfusca has a rather small simple spore; it emitted germinating 

 tubes from each end, and a septum across the middle of the spore appeared 

 after germination had taken place. Another experiment was with a much 

 larger muriform spore measuring 8o jx in length and 20 yu, in thickness. On 

 germination about 20 tubes were formed, some of them rising into the air at 

 once, the others encircling the spore, so that the thallus took form imme- 

 diately; growth in this case also was centrifugal. In three months a diameter 

 of 6 mm. was reached with a thickness of i to 2 mm. and showing a differen- 

 tiation into medulla and cortex. The hyphae did not increase in width, but 

 frequently globose or ovate swellings arose in or at the ends, a character which 

 recurs in the natural growth of hyphae both of lichens and of Ascomycetes. 

 These swellings depend on the nutrition. 



1 MSUer 1887. 



