for the advance of Botany. 123 
execute. A great multitude of dissimilar products are elaborated 
and secreted by some one or other of these organs, but we know lit- 
tle or nothing concerning which of them it is that produces each 
separate result. Even the manner in which the imbibed nutri- 
ment is conveyed from the root to the leaf is not satisfactorily de- 
termined the functions of the leaf itself are not so well establish- 
ed as to be placed beyond all doubt; or rather, the manner in which 
these functions are performed is not yet well understood. The re- 
searches of Robert Brown and Ad. Brogniart have settled, beyond dis- 
pute, some of the most important preliminary phenomena attending 
the fertilization of the ovule, but the ultimate facts are still to be 
discovered, and at present we have only conjectures and opposite hy- 
potheses between which we are to choose when we would inquire 
how the embryo may have originated, after the pollenic tubes have 
penetrated down the style into the ovarium. It seems indeed to be 
all but proved that these tubes really attach themselves to the fo- 
ramen, a circumstance which would appear to favour the somewhat 
mechanical theory of the introduction of the pollenic granules them- 
selves into the nucleus. Hitherto, the fact of a general circulation 
of the proper juices, or latex, in plants, through a peculiar system 
of anastomosing vessels, has only engaged the attention, or even met 
the observation of very few persons, except the original discoverer. 
The mode in which the assimilation of new materials takes place 
during the development of the trunks of trees cannot be consider- 
ed as satisfactorily determined ; the most favoured theory on the 
subject (that of Du Petit Thouars) requiring the confirmation of di- 
rect experiment, as well as the removal of very serious objections. 
But besides such inquiries as these, which need great delicacy of 
manipulation and considerable experience in the use of the micro- 
scope, there are many others which are within the reach of every one 
like that question, so important in agriculture, lately started by 
De Candolle, whether the excretions from the roots do not deterio- 
rate the soil, as respects other plants of the same or allied species, 
but actually improve its qualities for those of different families. 
The agriculturist who wishes to prosecute this, or any research of 
interest in a physiological point of view, must remember the sound 
advice which De Candolle has given always to perform a series of 
comparative experiments, by which means alone he can hope to check 
that liability to error, against which the most accurate judgment 
is no safeguard, whilst it relies only upon its natural unassisted 
powers. 
In thus briefly noticing some of the more important topics which 
