370 CALIFORNIA ACADEMY OF SCIENCES. 



fruit trees are grown to the exclusion of other species, 

 forming, so to say, a forest of then- own. 



We will at present refer to a single group of insects, 

 the Coccides, and especially the species of Lecanium and 

 its allied genera, which in common life are comprised 

 under the name " scalebug." All these insects produce 

 a sticky exudation, which partly hardens into the pro- 

 tecting scale from which the group received its vernacular 

 name, partly it covers leaf and branch in form of a kind 

 of viscosity. 



This viscosity again retains the spores of minute para- 

 sitic fungi of different varieties, one of the most common 

 forms being the Capnodium, and we soon will observe a 

 sootlike substance covering many leaves in our orchards 

 as a concomitant of the scalebug. Under ordinary cir- 

 cumstances but few spores out of a million reach their 

 destination, that is a spot favorable to their development. 

 But with the facilities offered by the sticky surface of 

 leaves that are infested by the scalebug and the numbers 

 of individuals that have already developed and have ma- 

 tured their spores, the number of germs floating in the 

 air becomes such that the chances for the development 

 of the parasites become more and more favorable: and 

 as the Capnodium, the vegetable parasite, is but little de- 

 pendent on the species of plant on which it develops, it 

 soon begins to infest the forests, as well as orchards and 

 hedges. 



As most of our forest trees, being evergreen, never 

 shed their leaves at once, the foliation of these ever- 

 greens has ample time to foster and breed on their sur- 

 faces, roughened by Lecanium and Capnodium, other 

 fungoid growths, more detrimental to vegetation than the 

 unsightly but comparatively harmless Capnodium. 



Forms of Uredo will pass their dimorphic stage there, 



