128 DISEASES OF TREES 



characteristic of this parasite, still I cannot doubt that these 

 filaments with clamp cells belong to it. However, I will not 

 maintain this as an absolute fact, especially as clamps do not 

 occur either in the interior of plants or in the mycelia pro- 

 duced by germinating spores of Rhizina. 



My first cultures were undertaken on August iQth, 1890, with 

 fresh spores, which I sowed partly on a gelatine extract of 

 fruit and partly on humus sandy soil. These produced no 

 result. 



On repeating the culture with numerous spores on Septem- 

 ber 1 8th, only a single one germinated. On the other hand, 

 germination was general in twenty-four hours in a seeding on 

 gelatine extract of fruit which was undertaken on November 

 1 8th. These germinating spores are shown in Fig. 64, b. The 

 extraordinarily thick germ-tube proceeded from the lateral 

 wall of the spore, and from the first its diameter was as 

 great as that of the spore itself. After only forty-eight 

 hours the germinating spore had reached the stage which is 

 represented, slightly magnified, in Fig. 64, c. 



The stout much-branching mycelium is septate, and resembles 

 in every respect that which is found penetrating the healthy 

 cortex of slightly or much-diseased plants. Under such circum- 

 stances it grows between the cells of the parenchymatous 

 tissues, while in the soft bast its progress is partly intercellular 

 and partly intracellular, the sieve-tubes being frequently packed 

 full of a dense filamentous mycelium. In the process of time 

 the mycelium kills the tissues of the cortex and soft bast, whose 

 elements become brown and completely dismembered, or, in other 

 words, isolated. The development is so luxuriant that it forms, 

 in certain places, a pseudo-parenchymatous fungus-tissue, consist- 

 ing of vesicular swollen cells. This however is speedily destroyed 

 as soon as the tissues between the wood and periderm become 

 almost completely decayed. In this process of decay very 

 minute organisms resembling Micrococcus play an important 

 part. When employing^ high power, the whole field of view 

 sometimes swarms with these minute cells, whose diameter does 

 not exceed I to i'5 micromillimeters. These originate (Fig. 70) 

 on very small stalks resembling sterigmata, which project some 

 from the lateral walls and some from the apices of the fila- 



