PLANT DISEASES AND KUNCI. 2g 



has the power, in greater or less degree, of destroying all the vege- 

 table parasites which infest the skin, such as the different forms of 

 ringworm. When applied to the ' thrush ' of early infancy sulphur 

 rapidly effects a cure, as I have found in a number of cases, etc." 

 Now all these diseases of the human subject are attributed to the 

 action of external fungus parasites, and, in all, the same remedy as 

 that found beneficial for epiphytal fungi has been employed with 

 success. 



The other class, or endophytal, are more numerous, insidious, 

 and less subject to external treatment. The disease is present in 

 the tissues long before it makes its appearance on the surface, or 

 even before it produces a sickly habit, and when at length the pres- 

 ence of the foe is unmistakable, all the mischief has been done, 

 and the infested plant is more or less permeated with the disease. 

 To this class belong the corn rust and mildew, the potato disease, 

 the apple scab, and a host of other destructive agents. 



The modes by which these internal parasites perpetuate their 

 species are rather elaborate, and must be taken into account in all 

 attempts to combat them. The rotting moulds of the genus Pero- 

 iiflspora generally produce a speedy decay of the tissues, as, it may be 

 believed, by a kind of fermentation. The initial conidium, or spore, 

 is elliptical and uncoloured ; the contents are at first granular, then 

 they become divided into four parts, each of which is gradually 

 surrounded by a thin membrane. When matured, the membrane 

 of the mother cell is ruptured, and the four daughter cells are set 

 free, each furnished with a pair of movable cilia at one extremity, 

 by means of which they are capable of active motion in a thin film 

 of moisture, such as would lie upon the surface of a leaf after a 

 shower. After a short period of activity these little zoospores come 

 to rest, the cilia are absorbed, and they commence germination by 

 the protrusion of a delicate thread, which enters one of the stomata 

 of the leaf, and becomes the first thread of mycelium, in the interior 

 of the tissues of the plant, which is thereby infected. Ultimately 

 this mycelium, being largely increased, sends up erect threads 

 through the openings of the leaf, such threads being usually much 

 branched towards the apex, and bearing at the top of every 

 branchlet an elliptical conidium or spore, just like the original 

 conidium with which the series commenced. Each of these spores 

 falls away when mature, either upon the supporting leaf or upon the 

 ground, and then the differentiation into zoospores, and all the sue- 



