PATHOLOGICAL COX DIT IONS 89 



the disease is generally associated with abnormal moisture conditions. 

 Trees subject to poor drainage, underlaid with hardpan or subject 

 during the previous season to extreme drought or to an irregular water 

 supply are most subject to the disease.'*^ Drought, therefore, must be 

 regarded as an important contributing factor. Other than the dying 

 back of the limbs, this disease presents a number of well defined symptoms 

 in citrus trees that may be mentioned as further illustrations of the dis- 

 turbed and pathological conditions which may arise from, or be end 

 products of, an abnormal water supply. Among them are: the produc- 

 tion of gum pockets, stained terminal branches, ammoniated fruits, bark 

 excresences, multiple buds, exceptionally deep green color of the foliage, 

 the production of S-shaped terminal shoots and of coarse leaves somewhat 

 Hke those of the peach in shape. •*'■* 



Cork, Drought Spot and Related Diseases. — Under these names have 

 been described numerous disorders of fruit trees that are apparently 

 related. Indeed differentiation between them is frequently difficult, if 

 not impossible. This is understood easily because they are in fact 

 closely related and are perhaps only different symptoms of the same 

 fundamental disturbance in the physiology of the plant. The following 

 descriptions are from the reports of those who have made a close study 

 of them. 



Fruit-pit. — " In the early stages of fruit-pit one finds numerous sunken areas 

 from 2 to 6 millimeters in diameter on the surface of the apple. These 

 depressions are somewhat hemispherical in shape and have the appearance of 

 bruises. At this stage the spots are not brown and often show no difference in 

 color from the surrounding surface of the apple. . . . Later they begin to take 

 on a brown tint, but at first this seems to show through from rather deeply 

 seated tissue and not to arise from any discoloration of the epidermal or imme- 

 diately underlying cells. Sections of such spots show that this is the case, and that 

 the browning and shrinking of the cells occur in the pulp of the fruit and in the 

 tissue that is transitional between it and the hypodermal parenchjona. 

 Later the surface cells also become dark brown. ... As the disease advances 

 spots situated near each other often become confluent, developing into one large 

 spot. In all such cases examined it was found that the original spots were 

 closely connected with one vascular branch. . . . The surface spotting is often 

 accompanied by browning of the tissue immediately surrounding the vascular 

 bundles. Upon cutting such an apple one sees numerous apparently isolated 

 brown spots. Further study shows that these are not isolated but are in reality 

 continuous strands of brown tissue surrounding the vascular bundles. The 

 portion of the vascular system that is most commonly affected is that lying 

 within fifteen miUimeters of the surface of the apple. The surface spots often 

 occur without the internal browning and also the internal browning may occur 

 unaccompanied by any surface derangement. "^^ 



Cork. — Cork is most commonly observed when the apple is anywhere from 

 half grown to nearly mature. It may be briefly characterized as internal brown- 



