1917] DISEASES OF PLAXTS. 455 



place through the wall of the root hair while the organism is in a uninucleate 

 stage. The root hair at once shows hypertrophy. The amoeba increases in 

 size as it passes rootward, and finally, l)y direct cell-wall penetration as well 

 as by the division of the host cells, the pathogene is distributed throughout the 

 cortical tissue. Aside from P. hrassicce there is said to be often present another 

 organism which causes no hypertrophy and which is probably Olpidium 

 brassier. 



In the experiments to determine the relation of bacteria to P. hrassicce, as 

 claimed by Pinoy (E. S. R., 14, p. 946), all the results obtained indicate that 

 the bacteria do not enter the host as soon as the slime mold does, but follow 

 only after there has been a rupture of the epidermis. Consequently the bac- 

 teria can be of no vital importance in the nutrition of the parasite. 



Bitter pit investigation. — The experimental results in their relation to 

 bitter pit and a general summary of the investigation, D. McAlpine (Rpt. 

 Bitter Pit Invest. [Aust.^, 4 (1914-15), pp. 178, pis. 4I, figs. 2).— This is the 

 author's fourth report on this work (E. S. R., 33, p. 852), and sums \ip the 

 results of the study carried on by him for four years imder appropriations by 

 the Commonwealth and State governments of Australia. 



The causation and prevention of the disease by direct measures received the 

 greater portion of attention, as breeding experiments were precluded by the 

 time limitation imposed. Extended investigations failed to connect the disease 

 with any parasitic organism. It is claimed to be due to a disturbance of the 

 normal functions of the plant itself. In some apple varieties, the majority of 

 the trees showed a tendency to the pitting habit, and some individual trees 

 showed bitter pit to the extent of 60 or 80 per cent of their crop. Abundance of 

 material was obtained from the six States included in the investigation. 



It is held that success against bitter pit depends entirely upon the ability 

 of orchardists to control the conditions in the individual trees, and the ability 

 of shippers to control conditions, chiefly temperature, during transit. Ap- 

 parently, the factors operative in the production of bitter pit include every 

 phase in the life of the tree, from the nursery to the marketed fruit. The ex- 

 perimental work is reported in considerable detail and the practical applica- 

 tions of the results obtained are pointed out. It appears that apples appar- 

 ently faultless can be shown, by means of the X-ray, to be affected, the honey- 

 combed appearance of a pitted apple contrasting sharply with the solid flesh 

 of a healthy fruit. Apparently the disease begins on the tree and continues to 

 develop under certain unfavorable storage or shipping conditions. 



Biochemical researches were conducted by Rothera, Jackson, and Kincaid. 

 The absence of development of bitter pit in apples kept at 32° F. is thought to 

 be simply the usual phenomenon of arrest due to slowing up of all vital activities 

 at that temperature, as nothing indicates a permanent influence of such 

 temperature on this disease. It appears that the pitting of applies is de- 

 termined before they are picked and before their starch is converted into 

 sugar, though laboratory experiments indicate some possible influence of treat- 

 ment (as handling) after picking. Further work needs to be done in this con- 

 nection. 



Other studies were conducted in cooperation at various points by different 

 persons, who are named. Susceptible and nonsusceptible varieties were com- 

 pared as regards the composition of the fruit and the nature of the leaf, since 

 it appeared evident that retardation in the leaves v.-ould result in increased 

 transportation of water to the fruits. Yates, which is nearly immune, appears 

 to be more nearly allied to the wild crab apple than is the susceptible variety, 

 12883°— 17— No. 5 5 



