394 BOTANICAL GAZETTE [NOVEMBER 
production in the parent. Two hypotheses are offered to account for the 
appearance of these two types among the seedlings: (1) that they are muta- 
tions meee as a result of traumatism in accordance with the views of 
LARINGHEM; and (2) that the ordinary horseradish is not a natural species 
as serigie believed by taxonomists, but a hybrid, and that the two types 
of offspring produced from the seeds are partial or complete returns to its 
parent types. The author inclines to the latter view, and would interpret 
the sterility of the horseradish as due, not to the accentuated development 
of fleshy roots, but to a weakening of the sexual development, not infrequently 
found in hybrids. The reviewer is inclined also to the latter interpretation, 
and would point out the important bearing the author’s method of securing 
seeds of the horseradish may have in its application to other sterile hybrids. 
Many experiments have been terminated by the failure of hybrids to produce 
seeds. It may be that some of these cases will yield to methods of treatment 
similar to that employed by BrzEzINsKI in securing seeds of horseradish.— 
Gro. H. SHULL. 
The ecology of conifers——Srorres and Moss have discussed the xerophyt- 
ism of conifers, and now Groom® considers a number of their ecological 
features. In the introductory statement three problems are outlined: the 
cause of their xerophytic foliage and tracheidal wood, the cause of their 
survival in competition with dicotylous trees, and the cause of the suppression 
of many forms in past ages. Groom correctly concludes that not all conifers 
are a in spite of their xerophytic leaf structure, calling attention ” 
von HOuNEL’s demonstration of high transpiration in the larch, and to 
own poeta which show that coniferous wood, in spite of its srectial 
structure, may conduct water with a rapidity equal to that of a rapidly tran- 
spiring dicotylous tree. Attention is called to the fact that the aggregate 
leaf surface of a coniferous tree may exceed that of a dicotylous tree, because 
of the immense number of leaves. Indeed, Groom regards the xerophytic 
structure of the leaf as a necessity in view of the great amount of expo 
surface, and he applies the term “architectural xerophytism” to xerophytism 
that is dependent upon the organization of the plant rather than upon the 
direct influence of external factors upon the organs in question. In opposi- 
tion to Stopes, Groom regards the tracheidal nature of the wood as a feature 
of advantage rather than a feature necessitated by heredity, and notes that 
similar wood tends to occur in various evergreen dicotyls. The extinction 
of many conifers of past ages is attributed to their imperfect acclimatization, 
to the fact that they have a great number of insect and fungus enemies, 
and to their relatively slight power to react advantageously to new conditions. 
However, their architectural xerophytism makes it possible for them to thrive 
in nearly all situations, from those that are physically or physiologically dry 
8 Groom, Percy, Remarks on the oecology of Coniferae. Annals of Botany 
24:241—-269. Igto. 
