334 BOTANICAL GAZETTE [APRIL 
Fusarium oxysporium and Verticillium albo-atrum. In order to determine the 
rice of transmission of these wilts through seed tubers, McKay® has 
rried on experiments with numerous varieties of potatoes for four years. 
Verticillium albo-atrum occurs somewhat more extensively in small tubers than 
in medium-sized ones, 30~50 per cent of the crop grown from infected seed 
tubers being diseased with Verticillium wilt, as shown by cultures. Fusarium 
oxysporium is transmitted in a lesser degree, and it appears to be capable of 
remaining virulent in the soil for several years after the production of a crop 
of potatoes. Vascular discoloration is an unreliable index of Verticillium 
infection, since approximately 7-17 per cent of cultured tubers which produc 
the fungus show no discoloration, and 55 per cent of the tubers which show 
brown vascular discoloration give no organism parasitic for the potato. 
Although the discoloration occurs at the stem end of the tuber, stem-end seed 
pieces give no more disease than eye-end pieces of the same infected tuber. 
Numerous species of Fusarium and other fungi mostly saprophytic in nature 
appear in cultures of wilt diseased tubers.—J. G. Brown 
Colloidal hydration.—In two recent papers MacDoucGAL®”? discusses the 
effects of bases, salts, and other substances on the hydration capacity of pre- 
pared colloidal bodies and masses of vegetable cells. In a previous paper™ he 
had reported that o.o1 N hydroxides retard the hydration of colloids, and sug- 
gested that the chief function of the base forming metals required by plants 
might be the restricting or limiting of the hydration capacity of the living proto- 
plasm. He now finds that when concentrations of 0.001 to 0.0001 M solutions 
of chlorides and nitrates, and 0.001 to 0.0001 N hydroxides are used, con- 
centrations comparable to those occurring in living cells, the hydration is 
increased and not restricted. He therefore reinterprets the function of the 
metallic elements as accelerators of hydration and growth. Correction is also 
made regarding the effects of HCI. Ata Px value of 4.2 the acid is now shown 
to cause more swelling than water. Some interesting studies of the hydration 
of roots of different ecological types, and of roots grown in different types of 
soil are reported. In general he concludes that all substances which are known 
to facilitate growth in plants will at appropriate concentrations increase the 
hydration capacity in some of the colloidal objects tested. —C. A. SHULL. 
Vertical distribution of Fucus.—Fucus has long been regarded as charac- 
teristic of the zone of tidal play, largely because of its high light requirement 
® McKay, B. M., Transmission of some wilt diseases in seed potatoes. Jour. 
Agric. Res. ae 1g2t. 
9MacDoveat, D. T., Water deficit and the action of vitamines, amino- 
compounds, and ge on hrdintion. Amer. Jour. Bot. 8:296-302. 1921 
70. The action of bases and salts on biocolloids and cell masses. Proc. 
Amer. Phil. Soc. 60:15-30. 1921 
Ir 
, Growth in organisms. Science 49:599-605. 1919. 
