MICROSCOnC INVESTIGATIOX. 197 



bnrk aud ruoiy. My obyeivuiiuiis seem Lu couliim ihe'sc coiumoii ru- 

 mors. 



In receiver No. 5 the liealtby bark was not contaminated, seemingly, 

 with the Ncemaspora, notwithstanding its immediate contact dnring 

 several weeks with the unhealthy bark. As might be expected, the 

 common molds, PenicilUum aud Mucors, grew all over the surface of the 

 specimens, healthy and unhealthy. The leaves in Nos. 3 aud 4 were 

 next examined. They had been subjected to the same treatment as the 

 bark. The healthy leaves, although confined during four weeks in a 

 moist atmosphere, at a temperature ranging from 80^ to 90'^, exhibited 

 no signs of mildew. A split uranch to which the leaves were attached 

 exhibited a small portioi* of Miicor fruit, and xdycdium on the sap- 

 wood and pith ; but the unhealthy leaves were completely covered in 

 two weeks with Mycelium^ (mold,) and the fruit of the common blue, 

 yellow, and black FcnicilUuni and Mucors. I have repeated these ex- 

 periments several times, always with the same results. It is evident 

 that the healthy leaves possess an antiseptic substance, which prevents 

 the growth of the common molds on them. A portion of healthy aud 

 unhealthy lea^'es from the trees above mentioned was analyzed in the 

 laboratory to determine the respective amounts of moisture, organic 

 matter, and ash in them, aud gave the following results : 



Healthy peach-leaves : 



Moisture 29.20 



Organic matter 63. 22 



Ash 7.58 



100. 00 



Uuhealthy leaves : 



Moisture 30. 9 



Organic matter . ■. 59.4 



Ash 3.7 



100.00 



The fact of the absence of ash or solid matter and of the increase of 

 moisture in the unhealthy leaves, would of itself account for their greater 

 tendency to mold. Since leaves do not absorb earthy matter from the 

 atmosphere, it is evident that the cellular structure of the tree has in 

 some way failed to perform its functions -, for, had the ascending sap car- 

 ried with it potash, lime, or other earthy matter, the leaves would have 

 been stored with them, since the leaves have no power t(f evaporate 

 them. The deficiency of earthy matters in the leaves may also account 

 for the absence of ash in the fruit. If the theory is well founded that the 

 leaves elaborate juice for the growth of the fruit, the leaves being de- 

 prived of proper nourishment, the fruit cannot mature. It has been 

 long observed that trees affected with the yellows fruit earlier and ma- 

 ture prematurely, and soon decay. The presence of a larger amount 

 of sap in the unhealthy than in the healthy, indicates an earlier and 

 greater flow than in that of the healthy tree. The presence of watery sap 

 in the leaves, twigs, and buds would induce naturally an early growth 

 of fruit and premature decay. From these and other observations the 

 disease seems traceable to the body of the tree or roots. Applications 

 of washes in this case to the leaves would probably prove useless, but 

 if applied to the bark and roots might prove curative; and for that 

 puri)ose, judging from microscopic observations, I would recommend 

 the frequent application of hot lye as the best substance. 



