198 
NALORE 
[ DECEMBER 31, 1903 
ducing a non-scientific volume, which is embellished 
with fifty-four plates, fifty-three of which are coloured, 
and contains a full and useful introduction. With 
this, among the many other popular works on natural 
history recently published, we may look forward to a 
prospective time, when the general reading public, and 
lovers of animal life, will be sufficiently acquainted 
with the main aspects of general zoology as to enable 
them better to grasp the real import of the many con- 
clusions and theories—philosophical and otherwise— 
which have followed the great Darwinian conception. 
It may also be hoped that the narrative of life-histories 
of insects, now so frequently detailed and so easily 
consulted, may incite a further cultivation of economic 
entomology, a subject in which our American cousins 
still hold the field. 
Grandeurs Géométriques. By J. Pionchon. Pp. 128. 
(Paris :: Gauthier-Villars, 1903.) Price 3.50 francs. 
EXPERIENCE in the teaching of young engineers at 
Grenoble has induced Prof. Pionchon to undertake the 
task of publishing some seventy little volumes present- 
ing in a clear outline the fundamental notions, theo- 
retical and practical, which should form the basis for 
further study. The collection includes sections on 
mathematics, mechanics, physics, electricity, and 
economics, and the present volume is the fourth of the 
first section. It explains in an elementary way the 
nature of the different geometrical entities and the 
methods by which they are measured. There is no 
attempt to dip beneath the surface and introduce any 
of the philosophy of the subject, but some passages 
in smaller print give rather more advanced consider- 
ations and analytical formule without proof. 
If the book stood alone it could perhaps be passed 
without comment, but the prospect of seventy others 
of the same kind compels a word of criticism. It 
must be admitted that the contents appear to be per- 
fectly sound, but beyond this we have little praise to 
bestow. Whatever it contains of value ought to be 
in the notebook of every engineering student who has 
had the minimum necessary instruction in mathe- 
matics, and if it is not already there, the reading of 
this volume will only lead to that undesirable sort of 
knowledge which too often forms the main part of 
the mathematical equipment of engineers, and is un- 
fortunately encouraged by some of their teachers. The 
appearance of the pages suggests that they are de- 
signed to compensate physical as well as intellectual 
myopia, and this emphasises the inanity of many of 
the propositions. The author must be singularly 
devoid of the sense of humour. Rove Edel Ed 
LETTERS TO. THE EDITOR. 
[The Editor does not hold himself responsible for opinions 
expressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NaTuRE. 
No notice is taken of anonymous communications. | 
Secondary Radiation produced by Radium Rays. 
I vateLty had occasion to produce some radium radio- 
graphs of two partially overlapping pennies contained in 
a paper envelope which was laid directly upon the 
photographic plate. A print from one of the results 
shows that the shadow of the upper coin is blurred 
and diminished where the rays pass through air from 
the edge of this coin to the plate, but that it is sharp 
and of the correct size where the rays pass to the plate 
through the lower coin. This seems to point to the pro- 
duction of a considerable secondary radiation by the rays 
in their passage through air. L. R. WILBERFORCE. 
University of Liverpool, December 22. 
NO. 1783, VOL. 69] 
An Interesting Yucca. 
Ir frequently happens that facts of much general interest 
are published in systematic monographs and other taxo- 
nomic works, and are in consequence overlooked by many 
of those to whom they would be most valuable. Turning 
over the pages of the revision of the Liliaceous group 
Yuccez, published with superb illustrations in the 1902 
report of the Missouri Botanical Garden, I came across 
some statements which seem to deserve wider circulation 
and comment. The whole of the work referred to, by Dr. 
Wm. Trelease, is exceptionally well worth reading on 
account of the extremely lucid presentation of the facts, but 
the statements which especially interested me are as 
follows :— 
The subgenus Cheenoyucca contains thirteen species, some 
of which have the style green while others have it white. 
Yucca glauca is the very common narrow-leaved green- 
styled species of Colorado and northern New Mexico, ex- 
tending to South Dakota and central Kansas. The in- 
florescence is simple, or with an occasional branch. Yucca 
constricta is a white-styled species, very similar to Y. 
glauca, found from the Pecos River region of Texas to 
Seward County, Kansas, where it meets the range of 
Y. glauca. It has the inflorescence rather amply branched 
at the top. A few years ago Mr. James Gurney, head 
gardener of the Missouri Botanical Garden, ‘‘ was struck 
with the variety of foliage and difference of vigour of 
growth ’’ shown by the Yuccas of Seward County, Kansas, 
all being ostensibly Y. glauca. He collected a considerable 
number of these plants to show the differences, and they 
were transferred to the Missouri Garden, where some of 
them have bloomed. Among them was one which had 
practically the foliage of Y. glauca, but it produced ‘‘a 
rather ample long-pedunculate panicle of pure white 
flowers, with white styles,’? which began to expand at the 
end of the flowering period of Y. glauca. This specimen 
was by no means to be separated from Y. constricta. Other 
specimens exhibited the normal flowers of Y. glauca, and 
still others’ had flowers like those of glauca, but with a 
conspicuously branched inflorescence. ‘This last form agrees 
with the long-lost Yucca stricta of Sims, but is placed by 
Dr. Trelease as a variety of Y. glauca. In addition to 
these differences in the flowers, the foliage varied in breadth 
and flexibility. 
No suggestion is made by the author that the phenomena 
described are the result of hybridisation, but it is well 
known that Yuccas are frequently crossed in cultivation, 
and Dr. Trelease presents an extended discussion of Yucca 
hybridisation in another part of his paper. In the case of 
the Seward County plants, we have an unexpected and 
great mutability developing locally in an ordinarily stable 
species of wide distribution; and is it not suggestive, to 
say the least, that this should occur just where the ranges 
of Y. glauca and Y. constricta overlap, and that the so- 
called stricta should have more or less intermediate 
characters taken as _a whole, while the features taken 
separately are nevertheless pure? May this not be a case 
conforming with the Mendelian laws? In any event, it 
seems well worth consideration, for the mutability has to 
be explained somehow or other, that is to say, there must 
be a reason for it. 
Granting the supposed hybrid origin of Y. stricta, the 
case is curiously parallel to that of the perplexing wood- 
peckers of the genus Colaptes inhabiting the same region, 
which are intermediate between the eastern yellow-shafted 
and western red-shafted species. 
The only other Yucca which could be involved in the 
above discussion is the green-styled Yucca mollis (Y. 
angustifolia mollis, Engelmann, 1873),! but this is not 
known to extend so far west as to meet the range of 
Y. glauca. 
T. D. A. CockereLt. 
Colorado Springs, Colorado, U.S.A., December 13. 
1 Dr, Trelease names this ¥. arkansana, ‘‘in deference to the prevalent 
American practice in nomencla'ure.” whereby mod/is is held untenable 
because of Carriére’s prior V. gZoriosa mollis, applied to a garden form. A 
practice which permits a name proposed for a garden variety of a different 
species to stand in the way of an otherwise valid ‘specific name should 
urely be condemned. 
