= = 
Feb. 15, 1883] 
twenty years old, had all the sieve-tubes at its base still 
in a state of full activity. Ina stem of Yucca alotfolta, 
about fifteen years oli, the sieve-tubes of all the fibro- 
vascular bundles, even the innermost, were active, and 
had their sieves covered with callus; but this was no 
thicker in the oldest than in the youngest tubes. Ina 
stem of Dracena draco, at least twenty years old, the 
callus had nearly or entirely disappeared from many of 
the sieve-tubes; but the plant was otherwise in bad 
health. 
The callus is not a reserve-substance ; for in gymno- 
sperms and dicotyledons it often remains unchanged for 
years in the dead sieve-tubes, and even in leives which 
have fallen in the autumn, and in aérial branches which 
die in the winter. It behaves rather like a secretory 
product ; and this view is confirmed by the study of its 
development. The organised structure which the callus 
sometimes exhibits is not a sufficient objection to this 
view. 
- Under which class of organic compounds the callus 
should be placed cannot at present be determined with 
certainty. Its behaviour to iodine-reagents and to aniline 
blue appears to indicate an alliance with proteinaceous 
substances, and especially with nuclein ; in this respect 
it differs altogether from the solid carbohydrates, such as 
cellulose and starch. 
Allsieve-tubes resemble one another in their contents, 
at least as far as relates to the parietal protoplasm and 
water. The mucilage, which is undoubtedly a non- 
granular protoplasm, only exists in large quantities in 
dicotyledons ; no mucilaginous threads can be detected in 
monocotyledons or vascular cryptogams; in some mono- 
cotyledons there is simply an accumulation of mucilage 
in the sieve-tubes. The sieve-tubes of these two classes 
contain, on the other hand, a large quantity of smaller or 
larger refringent globules, which are also proteinaceous. 
Similar globules have been observed in the closed vas- 
cular bundles of Azppuris vulgaris. 
Although starch is almost always present in the sieve- 
tudes of open vascular bundles, it is seldom to be met 
with in those of closed bundles. The diameter of the 
starch-grains is always greater than that of the canals 
which are clothed with callus, which renders it impossible 
for them to pass from cell to cell as long as the sieve- 
tubes are in an active state. The reddish-violet or brick- 
red colour which these starch-grains take with iodine 
reagents indicates the presence of a diastase among the 
contents of the sieve-tubes. 
A series of observations on the same organs by E. 
Janczewski (Ann. Sci. Nat. xiv. 1882, Parts 1 and 2) 
was directed mainly to a comparison of their structure in 
the different primary groups of the vegetable kingdom. 
In vascular cryptogams the elements of the sieve-tubes 
are not much larger than those of the parenchymatous 
tissue. They have no nucleus, and contain proteinaceous 
globules, adhering to the parietal protoplasm, and col- 
lected below the pores. Both the lateral and terminal 
walls have a larger or smaller number of pores. The 
membrane of these pores is never perforated, and pre- 
vents the intercommunication of the contents of adjoining 
elements ; it is sometimes (as in Prer7s aguilina) pierced 
by callose cylinders. The time of year exercises no 
influence on the sieve-tubes, which remain in the same 
condition through the whole of their existence. 
In gymnosperms the life of the sieve-tubes may be 
divided into two periods, evolutive and passive. During 
the first period the pores in the walls of the young tube 
produce callose substance, and are transformed into 
sieves covered and closed by the callus ; the elements of 
the tubes contain, at this period, parietal protoplasm. 
During the second period the tubes entirely lose their 
protoplasm, and become inert ; but at its very commence- 
ment the sieves also lose their callus, and free communi- 
Cation is established between adjacent elements. 
NATURE 367 
In dicotyledons the structure of the tubes is still more 
complicated ; their life may be divided into four periods: 
evolutive, active, transitional, and passive. During the 
first period the cambial cell is not transformed imme- 
diately into an element of the tube, as in gymnosperms ; 
it divides longitudinally, and produces on one side an 
element of the tubes, on the other side one or two cells of 
the liber-parenchyma. In the elements thus separated, 
the pores of the walls, or the entire horizontal septa, 
become covered with callus, and perforated into true 
sieves composed of a delicate network of cellulose and a 
callose envelope. The tubes now enter the second or 
active period, characterised by the sieve-structure and 
the free intercommunication of the protoplasmic contents 
of adjacent elements. It may last for months or years. 
In some cases the sieves are closed before winter by a 
fresh formation of callus, and open again in the spring. 
During this period the tubes contain protoplasm, a larger 
or smaller quantity of a mucilaginous proteinaceous sub- 
stance, and sometimes starch. During the transitional 
period the tubes gradually lose their contents ; the sieves 
are closed by callus, and reopen again by the complete 
absorption of the callose substance. They have now 
entered the passive period; they are completely inert, 
and contain no organic matter ; the sieves are reduced to 
a delicate network of cellulose. 
The development and behaviour of the sieve-tubes of 
monocotyledons resemble that of dicotyledons, and their 
life may be divided into the same four periods. But 
from the fact of the vascular bundles being closed, and 
having no cambial zone capable of forming fresh tubes, 
the active period of the tubes may last as long as the life 
of the organ which contains them requires it. The 
passive period is, in fact, rarely manifested. In our 
climate the sieve-tubes have the power of closing their 
sieves in autumn, and reopening them in spring. The 
elements of the tubes contain no starch or mucilaginous 
substance ; and their parietal protoplasm only contains 
proteinaceous particles which seem to disappear in the 
spring, and to add to the density and refrangibility of the 
protoplasm. 
CASSELL’S NATURAL HISTORY* 
\\ the sixth volume, this well-illustrated account 
of the natural history of the animal kingdom is 
brought to a close, and the six handsome volumes leave 
nothing to be desired, so far as good covers inclosing excel- 
lent paper and beautiful typography are concerned. Indeed, 
the general get-up of the series is quite unexceptional, and 
as to the average value of the scientific contents we feel 
fully justified, on the strength of such contributors as 
Parker, Sharpe, Carpenter, Dallas, Sollas, &c., in strongly 
recommending the series to the majority of our readers. 
From a purely scientific point of view, we regret the 
title selected by the Editor. He should not have launched 
so important a book in these days upon the sea of science 
under an obviously wrong title. -The ‘‘ Historia natu- 
ralis” embraces, as the Professor of Geology in King’s 
College, London, well knows, something more than an 
account of the members of one of nature’s kingdoms, 
and of their distribution in space and time. It is there- 
fore certainly not scientific, and we take it as against 
modern culture to adhere to such a style. If, indeed, the 
eminent firm of publishers were to extend this natural 
history so that in another half-dozen volumes we should 
have an account of the equally interesting, and even more 
important vegetable kingdom, the title of the series would 
the more approach exactness. 
Although in the title of his work the Editor has followed 
in the footsteps of the mere compiler, he has by no means 
1 “Cassell’s Natural History.”” Edited by P. Martin Duncan, M.D. 
Lond., F.R.S., Professor of Geology, King’s College, London. Volumes 
1 to 6, illustrated. Volume 6. (London, Paris, and New York: Cassell, 
Petter, Galpin, and Co., 1883.) 
