138 PLANTS WITH TRAPS AND PITFALLS TO ENSNARE ANIMALS. 
Rotifera, small Acarina, species of Aphis, Podurids, &c., slip in. What it is that 
prompts them to visit these hidden chambers is as hard to say as it is to give the 
reason why the various species of Daphnia and Cyclops make their way into the 
bladders of Utrieularie. The most probable explanation is that the tiny creatures 
push into the cavities in their search for food, and there meet their death. 
It has been already stated that Zathrea is a parasite. Although we shall not 
discuss the plant in that capacity until later on, we must point out now that the 
main part of its nutriment is derived from the roots of deciduous arborescent 
Angiosperms by means of special suckers. It only grows in regions where the 
activity of trees and shrubs is interrupted by a winter of considerable duration. 
As soon as the woody plants on whose roots individuals of Lathrwa are parasitic 
acquire their autumn tints and shed their leaves, the suckers invariably perish. 
When, in the following spring, the ascent of the sap begins in the wood, Lathrea 
sends out new roots, which fasten their suckers underground upon the tree’s roots, 
the latter being turgid with sap. The nutriment supplied in this way to Lathrea 
is not essentially different from that taken up by the roots of the tree or shrub in 
question from the surrounding earth. It is composed mainly of water holding a 
small quantity of mineral salts in solution, a mixture which has been termed 
not unsuitably “crude sap”. 
Living underground and being destitute of chlorophyll, Lathraa has not the 
power of converting atmospheric carbon dioxide, or erude food-sap absorbed by 
the suckers from the tree or shrub attacked, into the various organic compounds 
necessary for further growth. For this reason, and inasmuch as the quantity of 
nitrogenous compounds in the fluids withdrawn from the roots is but small, every 
additional supply of organic food, especially of nitrogenous matter, such as is 
derived from captured animals, must be exceedingly welcome. Although the prey 
that is caught and digested consists for the most part of minute Infusoria, this 
addition must not by any means be undervalued. We must take into account the 
fact that every one of the innumerable leaf-scales of an individual Zathrea has an 
apparatus for capture and digestion, and that this apparatus is active throughout 
the entire year. The frost in winter does not reach so deep down in the soil as the 
place where the plant is imbedded, so that there, even at a season when above- 
ground everything is quiescent, the Infusoria and other little organisms continue 
their existence and may be captured by Lathrea. Thus, the extremely large 
number of animals secured in the course of a year is nearly sufficient to maintain 
the size of each individual plant. 
It is after all anything but strange that a root-parasite, destitute of chlorophyll 
and living underground, should make use of traps for animals, besides absorbing 
crude sap from other plants; but, on the other hand, we are naturally surprised to 
find plants which actually extract food from the earth by means of absorption- 
cells, also absorbing through suckers from roots in the capacity of parasites, and, 
furthermore, preying upon animals. An instance of such a plant is afforded, 
however, by Bartsia alpina. This remarkable organism is distributed in the 
