194 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
forms any xylem elements. Attempts to induce further growth by the 
removal of some of the roots from the rhizome resulted in the formation 
of new roots, but had no effect upon the activity of the cambium. 
Owing to the presence of this cambial layer and to the small number of 
vascular bundles, the root resembles that of a typical dicotyledon, but is 
like a monocotyledon in having one or two large vessels on the inner 
side of each bundle. The author believes that this root may be of 
special interest in connexion with the phylogeny of the angiosperms. 
S. G. 
Experimental Investigations on Birch and Oak. — Edith S. 
Whitaker ( Bot . Gaz., 1921, 71, 220-34,4 pis., 4 figs.). An account of 
an experimental investigation of the effects of wounding upon the rav- 
structure of Betula and Quercus. Angiospermous trees have three 
types of rays — namely, aggregate, compound, and diffuse ; the first of 
these appears to be the most primitive, and by different processes of 
evolution this type has given rise to the compound and diffuse rays. 
All wound-reactions occurring in woody tissues must be considered in 
relation to conservative regions, to seedling structure, and to fossil 
record, because only in this way is it possible to estimate whether the 
results of wounding are true reversions or not. It is found that all 
reactions are not true reversions, and extreme hypertrophy is unfavour- 
able to reversion. In Betula the wound-cap is large and hypertrophy is 
very marked, so that reversionary features are not found in this region, 
but in the cylinder opposite the wound. It is interesting to compare 
this result with that induced in Abies under similar conditions. In this 
case marginal ray-tracheids appear as in Betula in the region remote 
from the wound. In Quercus the wound-cap is small and there is no 
marked hypertrophy, and consequently reversionary features appear in 
the wound -cap itself. This result resembles the formation of traumatic 
resin-canals in the immediate neighbourhood of the wound-cap in Abies. 
The author points out that experimental investigations of this character 
are of interest not only from a biologic and pathologic standpoint, but 
also because they may show the possibility of producing new types of 
ornamental wood. S. G. 
Reproductive. 
Comparison of Development in Cuscuta and Convolvulus. — 
Gertrude E. Macpherson {Bot. Gaz., 1921, 71, 392-8, 3 pis.). A 
comparison of the development of the embryo of Cuscuta Gronovii Willd. 
and Convolvulus sepium L. The youngest embryo observed in Cuscuta 
consisted of a large basal cell surmounted by a smaller apical cell ; at a 
later stage the usual form is of an elongated and swollen base, having 
either no suspensor or a unicellular one. Later on both spherical and 
elongated forms are found, but there is no indication of plerome or 
periblem, nor of any differentiation into dermatogen. In the latest 
stages the embryo is large and well developed, coiled into spirals which 
lie in the scanty endosperm of the mature seed. The mature embryo 
bears two small scales, but except for some enlarged masses of undiffe- 
rentiated tissue on the sides of the embryos, there are no traces of 
