272 Meyen’s Report for 1839 on Physiological Botany. 
sary substances; it will always be the better if all that which 
it produced is left to it, for it is then manured not only by the 
vegetable matter produced, but also by the substances con- 
tained in the atmosphere, which mix with it in the form of 
dust dissolved as it were in the rain. After the introduction, 
the author treats largely of the external and internal structure 
of plants, or of the organs by which they exert their functions 
and procure nourishment, but this section must be desig- 
nated as altogether unsatisfactory, which, however, has no 
further influence on the practical value of the work ; it would, 
however, have been better if this part had also agreed with 
the present state of the science, for Vegetable Physiology has 
advanced so much in the last ten years, that it might have 
been presented in such a form as to have appeared both inter- 
esting and instructive, even to the practical agriculturist. The 
author has formed this section principally from the old 
(1827—1830) writings of DeCandolle, and now teaches some 
points which certainly DeCandolle himself has long since ac- 
knowledged to be erroneous; for instance, the root-spongioles, 
the ascent of sap in the intercellular passages, the excretions 
of the extremities of roots, by which plants are said to pre- 
pare their food, to kill others, &c. &c. The new experiments 
(former Report, p. 2) which have been instituted to ascertain 
the origin of nitrogen in plants, are looked upon by Spren- 
gel as quite conclusive, and he correctly remarks, that we can 
never hope to obtain a clear idea of the nutrition of plants, 
unless we call in the asistance of chemistry. The author 
observed, that plants growing on a soil containing much 
chloride of sodium, evolved, beside oxygen, also much chlo- 
rine, which seems to me to prove that the nitrates also are 
decomposed when in the plants, and that the manuring pro- 
perties of such substances may be explained in this manner, 
as has been already stated. To the functions of the leaves 
Sprengel reckons the following :—that they draw off from the 
other parts of the plants, particularly the young shoots, 
branches, and stem, the excess of fixed matters, on which ac- 
count they often contain ten times as much of these bodies as 
other parts; however, this phenomenon has been explained 
by later physiologists in quite a different manner; moreover, 
there are a great number of plants in which the bark of the 
stem contains most mineral matters. 
In another section Sprengel attempts to prove that a cer- 
tain quantity of mineral matter is necessary for the growth 
of plants ; the physiologists do not doubt this, but they ex- 
plain it differently. The reason why bulbs which are grown 
in water do not last two years, is, according to the author, be- 
cause the first time they are deprived of so much mineral 
