IIG 
BKITTSII PHARMACEUTICAL CONFERENCE. 
M'liat more compact and differently arranged; hence in proportion to amount 
of matter they do not expose so large a surface to the action of air and light 
as leaves, and as the process of assimilation only takes place in the cells im¬ 
mediately below the epidermis, their power of forming products and secretions 
is somewhat less intense, hut the difference between the parts immediately 
in contact with the leaves and the leaves themselves must be very slight. In¬ 
deed, I am by no means certain, but that the young herbaceous parts fre¬ 
quently contain quite as much, or even more active secretions than the leaves ; 
thus, if the latter organs be left on the stem till they have passed their active 
vital conditions, their secretions will have passed to a great degree into 
the young stalks in their passage downwards to the main stem, and hence the 
latter would be then probably more active than the leaves, as they v'ould in 
such a case not only be assimilating organs, but also the receptacle for the 
products and secretions formed in the surrounding parts. The most convin¬ 
cing proof that I can adduce of the capability of young succulent parts to 
form products and secretions, is in the case of Cacti, Euphorbias, etc., which 
have frequently no true leaves, but the plants are formed of a succulent 
stem or stems, from which the flowers arise ; nevertheless, as is well known, 
and in the case of some of the Euphorbias especially, the secretions pro¬ 
duced are of a ver^active nature. I might pursue this subject further, but 
enough has been said to show that in practice, in making preparations 
from herbaceous plants, we may consider the young vitally active parts in 
immediate contact with the leaves as not materially differing in activity 
from them, and that, consequently, they may be safely as well as econo¬ 
mically used with them. 
Again, a knowledge of the influence of solar light upon the process of 
assimilation shows us why plants, or parts of plants, when grown in the dark 
become blanched, and generally.deficient in products and secretions ; and the 
same fact explains Avhy the secretions of plants are less perfectly or more 
sparingly formed in cold dull summers than in light sunny ones, and the 
consequent greater activity of medicinal plants in the latter seasons. The 
same cause also explains why plants of warmer regions than our own are 
commonly remarkable for the more powerful nature of their secretions ; and 
also the reason why such j^lants when transported to this country and placed 
in our hot-houses can never be made, in consequence principally of the dimi¬ 
nished intensity of light to which they are then exposed, to form their pecu¬ 
liar secretions. We see, also, the cause why such plants as Celery, Endive, 
Sea Kale, etc., which, when grown under natural conditions, are rank and un¬ 
wholesome from the formation of their peculiar secretions, become, when 
cultivated under diminished light or in darkness, useful vegetables. 
All the above facts are of great interest, as they have an important bearing 
upon the growth of plants and fruits for the table, as well as in a medicinal 
and economic point of view. At present, however, much remains to be dis¬ 
covered before we can be said to have anything like a satisfactory explana¬ 
tion of the causes which influence the formation of the secretions of plants; 
for it is found that the same plants when grown in different parts of Great 
Britain, where the climatal differences are not strikingly at variance, or even 
at the distance of a few miles, or in some cases a few yards, frequently vary 
much as regards the nature and activity of their peculiar secretions. A 
striking illustration of this fact is mentioned by Er. Christison, who found 
that some Umbelliferous plants, as Cicuta mrosa (Water Hemlock), and 
CEnanthe crocata (Hemlock Water Dropwort), which are poisonous in most 
districts of England, were innocuous when grown near Edinburgh. The 
causes which lead to such differences are at present obscure, but the varying 
conditions of soil, moisture, and exposure to air under which such plants are 
