7o8 



FUNGI 



mycelium is parasitic upon potato tubers; it appears to injure 

 the latter and prepare an entrance for 

 bacteria of various kinds which sub- 

 sequently give rise to a ' wet-rot ' : 

 other parasitic fungi no doubt aid the 

 production of ' wet-rot ' in a similar 

 manner. 



(2) Fusarium disease: 'Dry-rot.' — 

 Just as there are several forms of 'wet- 

 rot ' disease, so are there several 

 ' dry-rots.' One form of the latter 

 Fig. 237.— a portion of the my- prevalent in many districts is due to 



celium oiFusariu/jt Solani. a Con- . 



idia in situ ; i detached simple the fUHgUS FuSariUm Solatli SaCC. 



conidium; c fully developed com- . r^* • r< j • -k r \ i-i 



pound conidia (enlarged about 300 \= I<UStSpOrlUni CiOlani Mart.) which 



diameters). .... 



IS probably an ascomycete, but only 

 known in a conidial state. The hyphae are septate and branched, 

 and the conidia at first single, oblong or oval cells, which when 

 fully developed become somewhat crescent-shaped and divided 

 into three or four cells by transverse septa (Fig. 237). 



The fungus can live a saprophytic life in the soil, but is also 

 capable of behaving as a parasite, attacking and damaging 

 the roots, stems, and tubers below ground in the late summer. 

 Usually, however, the effects of the fungus are not manifest in 

 the tubers until these have been stored some time, the disease 

 making its appearance just after Christmas. The tubers shrink 

 and the skin becomes wrinkled ; the contents within are changed 

 into a more or less hard, grey, crumbling mass, sometimes 

 resembling dry gritty chalk. 



The fungus is usually conspicuous on the outside of diseased 

 tubers in the form of small white spots of 'mould.' It most 

 frequently makes an entrance" through small wounds or cracks 

 on the surface, but is able to attack sound tubers when brought 

 in contact with them. The hyphae penetrate and kill the cells, 

 after which the cell-walls and protoplasm become brown and 



