508 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
periodicity of plants of temperate regions entirely an hereditary property, induced 
probably by physiological selection due to alternating conditions through a long 
series of years " ; whereas Sachs believed that the rest period is caused by a 
deficiency of soluble food, and the cessation of the rest is " due to a gradual 
production of enzymes." In the " Summary and Conclusions " the author gives 
his results : 
" The carbohydrate transformations during the rest period are entirely 
dependent upon changing temperatures. 
" Active diastase and invertase are present at all stages of the rest period. 
" There is no change during the rest period in the relative magnitudes of the 
forms of nitrogen." 
" Metabolism changes begin rather suddenly, and are concurrent with sprout- 
ing." 
" Drying causes rapid suberization of the skin, and greatly reduces the per- 
meability to water and gases." 
" Potatos may be sprouted at any time during the rest period by simply 
removing the skin and supplying the tubers with favourable growing conditions, 
which include in this case the maximum oxygen pressure of the atmosphere. 
The elimination of the rest period by this means is not due to water-absorption 
from the exterior. 
" Similarly, by cutting tubers into slices with a bud attached, this will sprout 
sooner. 
" It may be safely contended that the elimination of the rest period is cor- 
related with increased oxygen absorption." 
This means that the suberized skin prevents oxygen from being absorbed 
for respiration and metabolism. — G. H. 
Potato Tubers, The Value of Immature, as Seed. ByH. P. Hutchinson, B.Sc. 
(Jour. Bd. Agr. vol. xxiii. no. 6). — The account of a series of experiments at 
Garforth, Wye, and Midland Colleges, carried out to test a common and apparently 
well-founded belief that tubers lifted in an immature or unripe condition give 
better yields than tubers of the same varieties which have attained their full 
development. In every case, whether in plot or field experiments, the increased 
yield from immature tubers, usually lifted in mid or late July according to variety, 
was very marked. The plants were also more even and better in colour. Sugges- 
tions are made to account for this superiority, and it is suggested that it may 
be due to one or more of the following causes : — Tendency to select small tubers 
from ripe crop, a large proportion giving plants of medium and low productivity, 
the selection over a number of years emphasizing this ; thinner tuber coat in 
unripe " seed " rendering absorption of water in growth quicker ; amount and 
condition of reserve food materials, and the greater length of time in storage. 
G. C. G. 
Potatos, Clean Seed, on New Land in Southern Idaho, Experiments with. By 
O. A. Pratt (Jour. Agr. Res. vol. vi. No. 15, July 1916, pp. 573-575). — It is 
usually supposed that when disease-free potatoes were planted on new land, the 
resulting crop would be free from disease. Hence, when the first seed planted 
in new land in Southern Idaho were far from free of disease, it was naturally 
assumed that the diseases which appeared were introduced with the seed planted. 
The diseases most prevalent were wilt (Fusarium oxysporum Schlecht.) ; black- 
rot (F. radicicola Wollenw.) ; jeily-end-rot (F. sp.) ; powdery dry-rot (F. tricho- 
thecioides Wollenw.) ; Rhizoctonia, and common scab. 
The results obtained from experiments extending over two years show 
that : 
1 . Planting new clean seed potatoes on new land does not guarantee a disease- 
free product. 
2. A smaller percentage of disease may appear in the crop when clean seed 
is planted on alfalfa (lucerne) or grain land than when similar seed is planted 
on virgin or raw (uncultivated) desert land. — A. B. 
Potatos, Control of the Powdery Dry-rot. By O. A. Pratt (Jour. Agr. Res. 
vi. pp. 817-831, Aug. 1916 ; 1 pi.). — The powdery dry-rot of potatos is produced 
by the fungus Fusarium trichothecioides , which attacks tubers in the store and 
only through bruises. Badly diseased tubers fail to produce a plant, but slightly 
diseased ones do not affect the crop. The loss of stored tubers may be kept low 
by storing in dry, well-ventilated stores, at a temperature of about 35 0 to 40 0 F., 
or by disinfecting the stock before storage with a solution of 4 oz. mercuric chloride 
in 30 gallons of water, or formalin 1 pint to 30 gallons, provided the steeping is 
done within 24 hours of digging. The symptoms of the disease are a wrinkled, 
