10 



BULLETIN 395, U. S. DEPARTMENT OP AGEICULTURE. 



Fig. 3. — Longitudinal section of a lesion from 

 an Elberta peach twig of the current year's 

 growth, showing the early subcuticular de- 

 velopment of the fungus and a very early 

 stage of cork ^formation. Camera-lucida 

 drawing. (Magnified 310 times.) 



cork layers may be formed, before the final rapid swelling of tbe fruit 

 prior to its matmi-ity. In such cases stresses are set up and cracks of 

 varying sizes result. In many cases such openings are scarcely 

 macroscopic, but on badly diseased fruits, where the spots have 



become confluent, the cracks may ex- 

 tend across an entire side of the peach 

 and reach inward to the pit. 



Twig lesions. — In the early stages 

 of twig infection, slender, branching, 

 hyaUne, septate hyphss of the fungus 

 are found penetrating the subcuticu- 

 lar areas immediately exterior to the 

 cellulose waUs of the epidermal cells 

 (fig. 3). As the fungus develops, its 

 ramifications become more general, 

 its individual cells thicken, the un- 

 derlying epidermal cells of the twig 

 die, and the diseased areas are effec- 

 tively cut off from the sound cortical tissues below by layers of 

 cork cells. These corky layers are formed by means of tangential 

 divisions of the subepidermal cells. It is not unusual, however, for 

 the first division to be transverse, the daughter cells dividing tangen- 

 tially. The two or three actively 

 concerned hypodermal layers are, 

 in each case, rapidly converted 

 into a fairly uniform barrier of 

 thin corky cells of meager proto- 

 plasmic content. As the lesions 

 age and the epidermal cells be- 

 come more and more disorganized, 

 the outer layers of subepidermal 

 cells die and turn brown. 



After the advent of the dormant 



period of the host, the fungus con- Fig. 4.— Longitudinal section of a lesion from an 

 +iTmp«i to dpvplon thmncrhmit thp, Elberta peach twig of the preceding year's 

 tmues to aeveiop inrOUgUOUt tne gro,nh, showing the abundant subcuticular de- 

 fall, mild periods of the winter, and velopment of the fungus and the vigorous pro- 



thfi qnrinp- Thp mibnifimlflr hv- *^"°^'°'' °^ conidiophores m the spring following 

 tne Sprmg. ine SUOCUUCmar ny- infection. The host ceUs, which were badly 



phse increase in diameter and in disorganized, are semldiagrammatically repre- 



number until they form Stromate- ^^S Camera-lucidadrawmg. (Magnified 310 



oid layers which may extend over 



the entire lesions. While these structures may consist merely of 

 single layers of cells, they are usually thicker, often developing into 

 pseudoparenchymatous masses, six or eight cells deep (fig. 4). 



With the vigorous subcuticular development of the fungus, the 

 cuticle is often slightly raised and at times broken, while the remains 



