240 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
Primus Pseudo-cerasus. By R. I. Lynch {Gard. Chron. Aug. 4, 191 7, 
p. 47 ; with 4 figs.). — A critical note on apparently the only tree of this species 
. in cultivation in Britain. Reference is made to Lindley's type specimens in 
the Cambridge Herbarium in comparison with P. serrulata.—E. A . B. 
Puccinia graminis, Biological Forms of. By E. C. Stakman and F. J. Pie- 
meisel {Jour. Agr. Res. x. pp. 429-495, Aug. 1917; 7 plates). — Puccinia gram- 
inis has been found upon ihirty-five species of grasses in various parts of the 
United States. The authors have isolated the following biological forms from 
thirty grasses : Puccinia graminis tritici, P. graminis tritici compacii, P. graminis 
secalis, P. graminis avenae, P. graminis phleipratensis, P. graminis agrostis. More 
than one biological form may occur on the same host in nature, sc melimes even 
on the same, plant. On the basis of parasitism the biological forms may be 
divided into two groups, the first three forming group I. ; the other three, group II. 
The differential hosts for group I. are wheat, club wheat, rye, and Agropyron 
repens y while the differential hosts for group II. are oat, Phleum pratense, and 
Agrostis spp. 
Barley, rye, and Bromus tectorum have been infected by all six biological 
forms. These forms may be distinguished morphologically as well as parasiti- 
cally. The size, shape, and colour of the uredospores are the distinguishing 
characters. The rate of development of a given biological form depends upon 
the vigour of the rust strain, the kind and the age of the host plant, as well 
as external conditions of light, heat, and moisture. Sunlight, high relative 
humidity and moderate temperatures up to about 75° F. are most favourable 
to rust development. 
A short bibliography is appended. — A. B. 
Pueraria Thunbergiana. (Le Jard. vol. xxxi. p. 140 ; 1 fig.) — Pueraria 
Thunbergiana, the Kuzu or Kuza of Japan is a hardy and vigorous climber with 
handsome foliage and enormous tubers. It is valuable as forage, as a source 
of textile fibre and also of flour from its tubers. — 5. E. W, 
Quassln as a Contact Insecticide. By W. B. Parker (U.S.A. Dep. Agr., 
Bur. Ent. y Bull. 165, December 1914). — It has been supposed by many horti- 
culturists that quassia owes its effectiveness as an aphicide entirely to the 
extreme bitterness it imparts to the sprayed plants, making them thereby dis- 
tasteful to the pests. This undoubtedly plays a great part in its effectiveness, but 
the author has amply proved that Qaastin, the active principle of quassia chips, 
is a powerful insecticide itself, even when compared with nicotine sulphate. 
Methods of extraction are given, also experimental results in the field. 
C. P. C. 
Radioactive Substances as Fertilizers, Use of. By W. H. Ross (U.S.A. 
Dep. Agr. y Bur. Soils, Bull. 149, December 1914). — The results given in the above 
bulletin do not encourage the use of radioactive substances for general farm use. 
In fact, there is evidence given to prove that the increases shown in seme cases 
are due to the uranium contents, as the amount of radioactive substances in 
experimental fertilizer was actually less than that present in normal soils. 
It is thought, however, that when properly carried out, in greenhouse or 
other work where the great expense is justified, beneficial results may be obtained 
by the use of radioactive substances. 
It is found that nitrogen-fixing bacteria (Azotobacter chroococcum) were 
strongly stimulated in gelatine cultures, by passing air containing radium 
emanations over them. 
Under like conditions the period for the germination of seeds was shortened, 
and an increase of development in plant growth shown when watered by radio- 
active water. — C. P. C. 
Rainwater, Dissolved Oxygen in. By E. H. Richards (Jour. Agr. Set. viii. 
June 1 91 7). — The amount of oxygen carried into the soil as gas dissolved in 
rainwater is of considerable interest, since oxygen is essential for root aeration, 
and the oxygen dissolved in rainwater is also one of the chief factors controlling 
the activity of soil bacteria. The author has made a large number of analyses 
of rainwater by Vv inkier 's method, and finds that it is very nearly saturated with 
oxygen when the temperature of collection is below 5 0 C, as is the case for about 
nine months in the year in this country. For temperatures above 5 0 C. the 
dissolved oxygen may fall as much as 25 per cent, below the saturation point. 
/. E. W. E. H. 
