1096 The White Rot Disease of Onion Bulbs. [feb., 



Notwithstanding the most careful search during the last 

 two years the only method of reproduction which has been 

 observed is the germination of the above-described sckrotia. 

 It has been found, by means of artificial cultures in test-tubes, 

 that under suitable conditions of warmth and moisture these 

 bodies put forth ordinary vegetative filaments which develop 

 into a new growth of mycelium. The same method of germina- 

 tion, without doubt, takes place in the soil where the myceHum 

 produced would invade the roots of any onion plants which 

 were present. It would appear, therefore, that under natural 

 conditions the sclerotia formed on the diseased bulbs in the 

 summer remain dormant in the soil during winter, germinate 

 in the late spring, and thus bring about the infection of the 

 new crop. 



Shortly after germination the mycelium of the fungus pro- 

 duces minute conidia or so-called microspores.* They are 

 developed very freely in test-tube cultures, and were observed 

 also on diseased onions grown under field conditions. All 

 efforts to induce these conidia to germinate, however, failed. 

 Similar conidia are found in certain related fungi, and these 

 also have not been observed to germinate. Should they be 

 capable of germination under the influence of such conditions 

 as exist in the soil they would be of importance in that the fungus 

 would be provided with another and partially aerial method 

 of propagation.' 



In certain alHed fungi (e.g., Sclerotinia sclerotiorum on 

 potatoes, etc., 5. trifoliorum on clover, and 5. bulbormn on 

 hyacinths and other ornamental bulbs), stalked, cup-shaped 

 bodies known as ascophores, producing spores which are 

 actively discharged into the surrounding air, are developed 

 from the sclerotia. These bodies have not been observed, or 

 induced to develop, in the case of the onion fungus. In order 

 to encourage their development the usual method of subjecting 

 the sclerotia to artificial freezing, in this way simulating 

 winter conditions, was repeatedly tried but without effect. 

 It would appear, therefore, that the disease is not spread by 

 air-borne spores, but solely through the agency of sclerotia. f 



Another point of great practical importance is the length 

 of time the sclerotia retain their vitaUty. It is impossible 



* Voglino also described these bodies, but in spite of the most critical search 

 no trace of the sphacelial stage described and figured by him as occurring on 

 the sclerotia themselves was observed. Dr. G. H. Pethybridge informs us 

 that this stage could not be detected in the material he examined in Ireland. 



t It is for this reason that the authors prefer to retain Berkeley's generic 

 name Scleroiium rather than to transfer the species to the ascomycetous genus 

 Sclerotinia, 



