SCIENTIFIC SUMMARY. 
429 
BOTANY. 
Insectivorous Plants. — M. Hochstetter argues in opposition to the opinion 
qmt forward by Darwin and adopted by many naturalists, that the insects 
captured by various plants serve them as nourishment. (“Wiirttemb. 
naturwiss. Jahreshefte,” 1878, p. 106.) He divides insecticidal plants into 
three categories: — 1, Those which emit a tenacious fluid from various parts 
to which insects stick; 2, those which possess special organs (pitchers, &c.), 
into which insects make their way, and are either drowned in a fluid con- 
tained in the cavity or prevented from escaping by hairs or other mechanical 
means ; and, 3, those which capture insects by means of irritable leaves 
or glandular hairs. 
The first group, which is very numerous, has never been supposed to 
derive any benefit from the captured insects. This is not the case with the 
second, including the pitcher plants, &c., for the insects drowned in the fluid 
contained in the cavities presented by their peculiar organs are believed to 
•aid in the nutrition of the plants. M. Hochstetter says that, so far as he 
knows, nothing has been ascertained in support of this opinion ; [but it has 
been shown that the fluid from those pitchers exerts a digestive action upon 
animal substances, and contains a principle related to pepsine, although, we 
believe, no one has attempted to show how the products of such digestion may 
be absorbed by the walls of the cavity]. M. Hochstetter says that his observa- 
tions on Nepenthes, Sarracenia, and Cephalotus show most clearlv that the 
pitchers of those plants which contain many dead insects die off much sooner 
than those in which none or few are to be found. 
It is in the third group that the most striking instances of supposed 
insectivorous plants are to be found. Of these it has been affirmed that, 
after insects are captured, the plants excrete an acid fluid at the points 
where they are in contact with their victims ; that this is allied to propionic 
acid and even contains pepsine ; and that by means of it the soft parts of the 
insects are digested just as if they were in the stomach of an animal. 
The author notices the peculiarities of the three genera, Prosera, Proso- 
phyllum, and Pioncea, upon which most of the observations in this direction 
have been made, and, whilst giving all credit to Mr. Darwin for his valuable 
investigations upon this interesting subject, urges certain objections against 
the view that the plants are nourished by the insects they capture. His first 
objection, that the leaves of plants are not organs for the reception of 
nourishment, does not appear to be of much weight. In the second place, he 
remarks that the insects captured by the leaves either dry up or putrefy ; and 
in the latter case, according to his observations, they do not produce better 
vegetation, but the destruction of the leaf-tissue implicated, as he has 
frequently noticed both in Pioncea and Nepenthes. In Prosera, however, 
stronger growth of the neighbouring parts of the leaf, sometimes perhaps of 
the whole leaf, does occasionally take place. But, says M. Hochstetter, we 
know that whenever vegetable tissues are exposed to friction, and especially 
when leaves are pierced by insects, or eggs are laid in their cellular tissue, 
cellular growths occur ; and he indicates that in Prosera, vesicular inflations 
-are produced on the leaves at the points where the insects lie. 
The fact that an increased secretion of fluid takes place from the glands of 
