1893.] Mr. P. Groom. On Dischidia Rafflesiana. 



51 



III. " On Dischidia Rafflesiana." By PERCY GROOM, M.A. Com- 

 municated by S. H. Vines, F.R.S. Received February 1, 

 1893. 



The Function of the Pitchers. — The pitchers contain living ants and 

 acari, small quantities of insect remains, considerable amounts of 

 earth, humus, and water ; but all these bodies and substances are not 

 found in each pitcher. The earth and humus, though partially 

 brought to the pitchers by the agency of rain-water, are mainly con- 

 veyed thither by ants, which nest within the pitchers. That the roots 

 within the pitchers utilise these solid matters is suggested by the 

 following facts, observed on living plants in the Botanic Garden, 

 Singapore : — 1. The roots are well developed in pitchers containing 

 a rich store of earth and humus. 2. Sometimes these solid substances 

 are arranged up the whole of one side of the cavity of the pitcher, in 

 which case the roots are more strongly developed on the same side ; 

 these phenomena, -in some cases at any rate, could not have been 

 occasioned by water having previously been distributed in the pitcher 

 in the same manner. 3. Particles of earth are found clinging closely 

 to the root-hairs, which are always well developed in the presence of 

 solid substances. Actual experiments on living plants prove that the 

 pitcher-roots can absorb liquids. The pitchers are not mere water- 

 reservoirs ; they are depositories for solids from which, by means of 

 the roots within the pitchers, the plant derives part of its nutriment. 

 Probably the evolution of the pitchers has been, to a great extent, 

 determined by the myrmecophilous habits of the plant. 



Structure of the Boots. — In the young state there is an epidermis, 

 many of the cells of which grow out to form root-hairs. The hairs of 

 the climbing roots are more numerous on the side towards the sup- 

 porting stem or branch of the host-plant ("ventral side"), where 

 they form a mycelium-like weft. The hairs of the roots within the 

 pitchers are more uniformly distributed, but are numerous and short 

 at regions where the root is in contact with the pitcher- wall or with 

 another root. The hairs of the pitcher-roots, and those on the 

 ventral side of the climbing roots, persist for a long time, and are 

 cuticularised : elsewhere the epidermis disintegrates. The epider- 

 moidal layer or exodermis is made up of cells, the walls of which are 

 cuticularised and lignified. The outer walls of the passage-cells of 

 this layer are thick, often possess pits, and are traversed by what 

 may be either radial canaliculi or radial rods of a substance differing 

 from the rest of the wall. Close beneath the exodermis of the pitcher- 

 root, usually separated from it by one layer of cells, are about six 

 bands of sclerenchyma ; these bands are absent from the climbing 



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