OF INSECTIVOROUS PLANTS 439 



come under the "roof" of a gland, and at the same time come in contact 

 with the gland itself, and adhere to it. The gland now secretes a slight 

 quantity of a sticky mucilage, which is more viscous than the other 

 secretion of the glands — the pitcher liquor, that is found even in unopened 

 pitchers. The mucilage dissolves that part of the insect-body which can 

 be utilized by the plant. When the surface of the gland becomes dry 

 by absorption, the undissolved insect -residue falls from the gland, and 

 is usually washed down by the pitcher liquor, either as its level rises or 

 through the swinging motion of the pitcher, or its leaf. The resulting 

 sediment consists for the most part of chitin. The glands on the border 

 of the level of the pitcher liquor come in contact with the insects in this 

 manner, and the cells of these glands show aggregation -phenomena in 

 consequence of the absorption of organic substances, while the cells of 

 glands above the level of the liquor, or beneath its level and merely 

 washed by it, usually have unclouded contents. 



When a number of gnats were placed in a pitcher, which was just 

 opening, they swam on the surface of the liquor and came in contact 

 with the glands at its level. The pitcher was emptied, a portion of the 

 glandular region was dried, and some gnats were placed on the dry place; 

 the secretion occurred only after the course of 4 to 6 hours, was sUght 

 in amount and insufficient to digest the insects, but dried up about them. 

 When an insect was wet with the pitcher liquor and then brought on the 

 dry place in the glandular region, very soon secretion of the mucilage, 

 digestion, and absorption took place, so that only the residue of chitin 

 was left at the end of 5 to 8 hours. The liquor, used for wetting the 

 insect, must not have been diluted by water; since water may enter the 

 pitcher during the watering of the plant, the liquor should be taken from 

 a pitcher from which water has been excluded by means of a cotton plug. 



Greenhouse plants are abnormal in that they usually contain only a 

 slight quantity of liquor, secreted by the glands; as a consequence the 

 greatest portion of the glandular region is not wet by the liquor. Fenner 

 used suitable control experiments in his research. 



From his own experiments, and from the observations of Goebel(ll) 

 (see above), Fenner draws the following conclusions: — 



(1) Normal pitchers, in which insects are found, contain a faintly 

 acid liquor (formic acid according to Goebel), which acts upon the glands 

 as a chemical stimulant when insects, wet with it, come in contact with 

 the glands. 



(2) The liquor thus gives rise to digestion, so that insect bodies, which 

 are saturated with it, can rapidly be dissolved and absorbed if they come 



