
cuticle. 
* 
Marcu 31, 1923] 

same law of variation, the Poisson series, was obeyed 
by the number of colonies counted on parallel plates. 
Statistical tests were devised which proved that, save 
for a small proportion of definite exceptions, the 
necessary perfection of technique was effectively 
realised (R. A. Fisher, H. G. Thornton, W. A. 
* Mackenzie, Annals of Applied Biology, vol. ix. p. 325, 
1923). In studying the exceptional cases it appeared 
that these fall into two classes, (I) an abnormally 
high variation which, when investigated experiment- 
ally, has been traced to certain bottom-spreading 
organisms isolated from soil from Leeds and from 
Rothamsted, and (2) an abnormally low variation 
ascribable to defective procedure in the preparation 
of the medium. Application of the same tests to 
_ other extensive series of bacterial counts showed that 
a similar approach to theoretical accuracy, though 
rare, had been obtained by Breed and Stocking in 
counts of B. coli in milk. It should be emphasised 
that all cases of departure from the theoretical law 
of distribution, which have been investigated, are 
associated with large systematic errors in the means ; 
_ for this reason simple tests are presented by which 
_ such deviations from the theoretical accuracy of the 
method can be detected. 
PrimuLas OF CENTRAL AsrA.—Mr. F. Kingdon 
_ Ward, who was referred to in NATURE of February 
17, Pp. 231, as returning to England after extensive 
travels in Central Asia, has been contributing some 
account of his previous (seventh) expedition in Asia 
in the Gardeners’ Chronicle since May 1922. These 
articles not only describe very vividly the first 
discoveries of many new plants, to be of interest 
afterwards to the British growers of novelties, but 
also frequently raise interesting general questions 
from the point of view of a keen observer of plants ; 
as, for example, the discussion in the issue of February 
1o (p. 80), as to the association of meal—a granular 
waxy deposit developed on the cuticle—and fragrance 
_ in the Primulas, and the observation that the Primulas 
found growing on boggy habitats are generally without 
_ meal. 
Tue Cuticte or Cotron.—A paper by R. G 
_ Fargher and M. E. Probert, in the Journal of the 
Textile Institute, vol. 14, pp. T49-T65, February 
1923, seems to represent a notable advance in our 
knowledge of the chemical composition of the plant 
Material extracted from American cotton 
by benzol, heating with superheated steam, was 
available from some very large scale experiments. 
This method opens up the possibility of hydrolysis 
during extraction, but the large bulk of material 
made available by the scale of operations has pro- 
vided very precise information as to certain con- 
_ stituents of the cotton wax, although doubt may 
remain as to the exact form in which they are present 
in the cuticle. A new alcohol, gossypyl alcohol, 
CssH,y,0, is identified and described, montanyl 
alcohol, C,,H;,0, present in smaller amount, is also 
described for the first time ; small amounts of ceryl 
and carnaiibyl alcohol were also found, and a mixture 
of phytosterols; little if any glycerol was present. 
Palmitic, stearic, and oleic acids were found in the 
free state, the sodium salts of montanic, cerotic, 
palmitic, and stearic acid were identified, as well as 
the salt of an acid, C,,H,,O,, oleic acid and a lower 
isomeride of oleic acid were present as esters, but 
the proportion of unsaturated acids, either free or 
combined, was small. While this work, on one hand, 
will throw much light on the problem of scouring 
cotton, on the other, it gives much needed informa- 
tion ~ to the chemical constituents of the plant 
cuticle. 
NO. 2787, VOL. 111] 
NATURE : 
443 
Tue IsorTacE&.—Norma E. Pfeiffer has published 
a most valuable systematic study of this family in 
the Annals of the Missouri Botanical Garden (vol. 9, 
No. 2, April 1922). After a brief account of the 
morphology and ecology of the genus, which is in- 
complete as a bibliographical account of European 
work upon Isoetes, the species are grouped into sections, 
and keys are provided for the identification of species 
within the sections. Breaking away from former 
systematic studies, where habitat characters have 
largely been used for the establishment of main sub- 
divisions, the present sections are based upon the 
‘megaspore surface, whether tuberculate, spiny, 
crested, or reticulate. Within the sections great use 
is made of the lobing of the corms and the amount 
,of development of the velum ; megaspore characters 
are again frequently used, and eight plates are pro- 
_vided with photographic illustration of megaspores 
of different species. The family is a remarkable 
one to the student of plant distribution. Of the 
.64 species described, most are very restricted in 
range, the only exceptions being Isoetes Brauntt, 
\Dur., in North America, and I. lacustris and I. 
‘echinospora in Europe. Some of the Mediterranean 
.forms appear to the author to show close affinities, 
as though originating from a common stock; but, 
.on the whole, present knowledge of the species and 
their distribution is too puzzling, and probably too 
incomplete, to encourage premature speculation as 
to centres of distribution and evolutionary tendencies. 
It is interesting to find one submerged species—I. 
_echinospora—always without stomata while J. Brauntt 
always possesses some. 
. PuHysSIOGRAPHY OF Porto Rico.—A detailed study 
of the physical geography of the West Indian island 
‘of Porto Rico by Mr. A. K. Lobeck is published by 
-the New York Academy of Sciences (vol. i. pt. 4). 
It is the last section of a complete survey of the 
island undertaken by the Academy. The present 
part, which includes a large-scale map, is the out- 
come of field work in 1916-17. The physiographical 
history of Porto Rico appears to have begun with a 
complex mass of igneous rocks which were eventually 
reduced to a peneplain, except for two well-defined 
monadnock groups, now known as the Luquillo moun- 
tains and the Cordillera Central. No direct evidence 
on the horst nature of this ancient land mass was 
available. Uplift of the peneplain led to a new 
cycle of erosion, but only along the northern side of 
the island was a second peneplain produced. On 
the south the island was worn down less effectively, 
probably because of inadequate rainfall. Partial sub- 
mergence then allowed the formation of coastal plains 
on both north and south sides which, after uplift, 
were considerably dissected. Mr. Lobeck traces these 
events and discusses also recent changes now in pro- 
gress, illustrating his lucid paper by photographs and 
block diagrams. Some notes are added on the 
islands of Desecheo, Mona, Vieques, Culebra, and 
Muertos. 
PLIOCENE VERTEBRATES FROM THE TERTIARIES OF 
ArIzoNA.—On the initiative of the United States 
Geological Survey and with the co-operation of the 
United States National Museum, Mr. J. W. Gidley 
went early in 1921 to collect fossil vertebrates in 
the San Pedro Valley, Arizona, with the view of 
establishing the age of the deposits there, which 
until then had been termed Pleistocene. A _pre- 
liminary report has now been issued as Professional 
Paper 131-E of the United States Geological Survey. 
Unfortunately the material collected represents for 
the most part new species which cannot therefore 
be correlated with known faunas of other localities 
