ee a ee 
ECOLOGY 641 
Darwin' and others have experimented with the leaves on 
living plants of several Butterworts and found that drops of water, 
gum or sugar, and scratching of the surface of these leaves pro- 
duced no response, that insoluble solid bodies such as grains of 
sand and powdered glass allowed to remain for some time caused 
slight incurving of the margins and a slight increase in the quan- 
tity of mucilage secreted by the glands, but that when nitrogenous 
bodies such as bits of cartilage, meat, clotted blood, etc., are 
placed near the margin in contact with the glands they are excited 
and pour forth abundant mucilage and an acid secretion.. More- 
over, prolonged contact with these 
bodies caused a marked incurving of the 
margin which pushed them slowly 
toward the middle of the leaf where 
more glands are present and so increased 
secretion. This acid secretion com- 
pletely dissolved these substances which 
were later absorbed by the leaf. 
When small insects alight from the 
air upon the leaf of the butterwort, they 
become fastened by the mucilage and in 
struggling to extricate themselves only 
become deeper enmeshed by it. Within 
a short time the acid juice, secreted by 
the glands as a result of the stimuli, | 
digests their bodies and all excepting 
their hard, indigestible outer skeleta — P16. 482-—Pinguicula aul- 
: garis, a butterwort. An ex- 
(exoskeleta) is absorbed. tract of this plant containing 
If small creeping insects come upon a proteolytic enzyme is used 
the margin of the leaf they stimulate the in certain sedative expecto- 
: rant compounds. (After Le- 
edge to curl over and the marginal aie ad Dae 
glands to secrete. While the insect is 
enmeshed within the adhesive mucilage, it is slowly pushed by 
the curling up of the edges into the middle of the leaf where the 
acid secretion glands are most abundant. In about 24 hours the 
softer parts of its body are digested and absorbed and the leaf 
expands to its normal condition. 
1 Darwin: Insectiv. Plants, pp. 371-390, 1899. 
