174 MICROSCOPIC FUNGUS PARASITIC UPON THE CUCURBIT ACEjE, 



the pycnidia, and separate sporules which are sometimes found 

 in the joints of the necklaces of the conidia. (I). Oidium has 

 theoretically the same ; but really only produces two, conidia first 

 and at a considerable time afterwards sporangia with spores. 



Of the many plants of rock and water-melon and pumpkin that 

 I have examined, I have found none past the first or conidia state. 

 Indeed it is at this stage that the injury is done to the plant by the 

 exceedingly dense mycelium, which not only robs the leaves of 

 their moisture, but by forming a close mat over the underside of 

 the leaf, completely seals up the stomata. Tf we pick out from a 

 garden an apparently healthy plant, either of melon or pumpkin, 

 but upon which the fungus has really commenced its work, we 

 shall find that in this early stage, many of the leaves are marked 

 on the underside with dirty white spots, and that their edges are 

 beginning to curl inwards. In a day or two each spot will have 

 increased in size, and the effect will also be visible on the upper 

 surface of the leaf. At last the spots will have so much extended 

 their borders as to have become confluent, and the leaf will be 

 covered over its whole surface, by the mycelium of the fungus ; 

 becoming dry and crisp and easily reduced to powder if crushed in 

 the hand. Under the microscope, the appearance of this mycelium 

 is that of a very beautiful interwoven mat, studded here and there 

 with erect strings of conidia, resembling minute necklaces of pearls. 

 At this stage, any fruit that may be upon the same branch is lost, 

 although perhaps not larger than a small apple, by the decay of the 

 fruit stalk. There being no transpiration from the dead leaves, 

 any fluid that may still be passed upwards from the roots, appears 

 to be thrown upon the fruit ; and this being surcharged, while the 

 vitality of the plant is im pared or almost destroyed ; decay begins, 

 as in most other cases, at the articulations. The same thing occurs 

 in other plants. If for instance, we give a fuchsia a great excess 

 of water, *. e., more than it can get rid of by transpiration, in a 

 few days the leaves will become yellow and fall off if only lightly 

 touched with the finger, breaking at the articulations, and carrying 

 the petioles with them. 



(1) Berkeley Introd., Crypt., Bot., p. 78. 



