246 



THE FRUIT GROWER'S GUIDE. 



styles, preventing the pollen forming in the anthers, and the stigma from attaining such 

 position and formation as to favour pollenation. Thus the set of fruit is greatly 

 prejudiced ; in fact, the resulting fruit is more or less injured, and in some cases wholly 

 destroyed. 



On microscopic examination, fungi of the Oidium species are found to consist of a 

 woven mass of greyish- white mycelia or spawn threads upon one or both surfaces of 

 the petals or leaves, and on shoots, which much resemble a thin stratum of spider's 

 web, and this spawn is woven over the organs of transpiration (stomata), and the 

 trees are, as it were, suffocated. The mycelium is also furnished with minute suckers 



which hold on the leaves and other parts, and more or 

 less pierce and injure the cells. This piercing sets 

 up decay. Springing from the spawn threads are 

 numerous necklace-like clubs, and these are much 

 more robust on the softer under surface of the 

 petals, leaves, and tender growths than on the upper 

 surface and harder wood. This club-like growth is 

 the early condition of more highly developed fungi, 

 and distinguished as Oidium, well configured in the 

 illustration. 



Each oval body in the figure is a spore, capable, 

 upon germination, of reproducing mildew. The 



Showi n g:-ma S sedm y celia-nettedweb- g germinate more quick l y than the basal 

 like threads permeating pollen grains; club- 

 shaped bodies produced from spawn threads ones. Each bead-like spore is so slightly attached 

 each club a spore or seed; oblong-rounded ., i -i ,-\ ,-, -, -,i 



shapes-spores detached, two resting on a to lts nei S hb r that the least " breath of air sepa- 

 polien case in the centre of the figure. ra tes them. All are so potent with life that they 

 frequently germinate when standing in club form, others germinate as they float through 

 the air, and the spawn thread may be seen, under a magnifying glass, emerging 

 from the spore ready to invade any fruit tree it may fall upon that affords a suitable 

 nidus. 



The various mildews are included under the genus Oidium, but its species are known 

 to be merely a stage of fungi belonging to Erisyphe. Apple Oidium is believed to be 

 an early condition of Erisyphe communis ; peach mildew (Oidium leucoconium) of 

 Sphocrotheca pannosa; whilst vine Oidium (0. Tuckeri) has been traced to Erisyphe 

 communis. Oidium spores, though produced in inconceivable numbers, cannot survive 



Figr. 69. OIDIUM FAKINOSTJM GROWING ON 



POLLEN IN OPEN ANTHEBS OF APPLE 



BLOSSOM. 



