42 



JOUKNAL OF THE EOYAL HORTICULTURAL SOCIETY. 



on the damp surface of a leaf thev germinate readily, and the germ-tubes 

 may even pierce the epidermis, but infection does not follow ; whereas 

 when the germ-tubes have formed a vigorous mycelium in a nutrient 

 solution or in soil infection is certain. 



A series of Snowdrop bulbs were placed in suitable glass vessels so 

 arranged as to prevent the entrance of spores, and covered with sterilised 

 soil ; when the young leaves just appeared above the surface of the soil a 

 sufficient quantity of a nutrient solution of plum juice in gelatine wa i 

 added to reach about a quarter of an inch above the surface of the soil. 

 In one of these vessels conidia were sown on the surface of the nutrient 

 solution, and to another a quantity of vigorous mycelium formed by 

 conidia sown in a nutritive solution ten days previously was added. 



A certain number of leaves were removed daily for microscopic 

 examination after the introduction of the conidia and mycelium, and it 

 was found that in the vessel where conidia were placed ten days elapsed 

 before the mycelium attacked the leaves ; whereas in the vessel where the 

 ^igorously gro^^ing mycelium was deposited the leaves were attacked on 

 the third day. The above are the average results obtained from a series 

 of experiments extending over four years, and, it may be added, do not 

 demonstrate new facts, but simply corroborate the observations of I)e Bary, 

 who has already shown that the mycelium of certain species of Botrytis 

 can only attack li\'ing tissues after li\-ing for some time as a saprophyte. 



Experiments have shown that Snowdrops can be attacked at any age 

 by the Botrytis, but when the leaves are full-grown the mycelium can 

 only gain an entrance into the tissues below the surface of the soil. This 

 is effected by mycelium produced by conidia that have been carried by 

 ^\ind from other diseased plants growing in the neighbourhood. 



When a leaf is once attacked the mycelimn spreads in its tissues very 

 quickly, but I have never been able to trace the passage of the mycelium 

 do^n the leaves into the bulb, although I have repeatedly succeeded in 

 producing a rich growth of sclerotia on the bulb by bringing the latter 

 into contact with actively growing mycelium, and T am inclined to believe 

 that as a rule — if not always — sclerotia on the bulbs are formed from 

 mycelium present in the soil. 



The mycelium formed by sclerotia present on the bulb scales does not 

 pass directly from the scales into the leaves, but spreads upwards through 

 the soil, where it lives for some time, finally attacking the young leaves 

 just below the surface of the soil. Bulbs attacked by sclerotia when 

 grown in a glass vessel in a nutrient solution show this method of leaf- 

 infection very clearly, as the moment a hypha pierces the tissue of a 

 young leaf a minute brown spot appears, which continues to increase in 

 size as the mycelium cpreads in the tissues. 



When Botrytis conidia are sown in a nutrient solution germination 

 usually commences in about twenty hours ; the number of germ-tubes 

 produced by a conidium varies from one to four, these branch copiously, 

 the branches often growdng into each other and forming an irregular net- 

 work. The branches belonging to two or more neighbouring conidia also 

 often anastomose (6, fig. 4). After the culture has been growing for about 

 three days numerous densely tufted branches of hyphsp, or organs of 

 attachment, are formed (7, fig. 4). In one single instance conidia in a 



