420 REPORT OF STATE BOARD OF HORTICULTURE. 



APPEARANCE OF THE FUNGUS. 



Wherever it occurs the presence of this fungus is shown by the production 

 of clusters of ash-grey sjDores on the surface of the diseased tissues. In 

 passing through almost any of our prune orchards when the green fruit is 

 being picked, or even earlier, one ipay see here and there a prune that is 

 partly or wholly covered with this ash-grey or blue-grey ' 'mold. ' ' Occasion- 

 ally several such specimens may be seen hanging together in a cluster. If 

 one of these "moldy" prunes be examined it may be observed that the 

 " mold " occurs in clusters which are freqnently arranged in more or less 

 definite, concentric circles, although this arrangement is not so well marked 

 upon the prunes as upon certain other fruits. By the use of a small hand 

 lens one may determine that each of these clusters consists of immense num- 

 bers of minute thread-like projections which have burst through the epider- 

 mis. If a little of this "mold " be taken from the fruit and examined with 

 a higher power of the microscope, it may be seen that each of these minute 

 projections is composed of a number of very small oval bodies joined end to 

 end like a string of oval beads. 



THE SPORES. 



These minute bead-like bodies are the spores or "seeds"' of the fungus, 

 and every infested fruit is capable of producing hundreds of thousands of 

 them. Each spore is exceedingly minute. It is composed of a single cell 

 and is nearly colorless. The shape is generally oval, but both shape and 

 size vary somewhat. 



If some of these spores are placed in a perfectly dry place and examined 

 from time to time, it may be noted that they will remain for an indefinite 

 time apparently unchanged. We have examined such spores that had 

 remained for nearly two years without germinating — so long, in fact, that 

 they had lost the power to germinate, as was determined by numerous tests. 

 If other fresh spores are placed in fruit juice, or otherwise supplied with 

 moisture, and kept in a moderately warm atmosphere, it will be observed 

 that in a very short time (two hours or less) each spore will begin to push 

 out a delicate germ-tube. In other words, the spores will "sprout," and if 

 kept under favorable conditions the germ-tubes will grow so rapidly that in 

 from twenty-four to forty-eight hours they will in turn develop spores. We 

 may thus prove that heat and moisture are both essential to the development 

 of the fungus or brown rot. 



THE MYCELIUM. 



It is the germ-tube, which by continued growth, becomes the mycelium 

 of the fungus — the vegetative portion — which penetrates the tissue of its 

 host, and under the influence of which the latter assumes the characteristic 

 appearance of bi'own rot. This mycelium bears the same relation to the 

 whole fungus that the roots, stem, branches, and leaves of a higher plant 

 do to the entire plant. It is the portion which absorbs food materials and 

 assimilates them, and which eventually produces the reproductive bodies 

 or spores. 



