267 
Growth of Roots and Shoots. 
(. Hydrobryum olivaceum, and species of Dicraed), where the 
roots are developed as the most important organs for the 
assimilation of carbon dioxide, whilst the leaves are more or 
less rudimentary, and the stem is reduced to little more than 
the peduncle of the inflorescence. 
A contrast to the foregoing examples is afforded by those 
plants in which the stem and its branches are more or less 
independent of the root. Every plant-collector knows that 
in many species of Sedum , the leafy branches continue to 
grow for a time after the plants have been placed in the 
herbarium, unless they have been previously killed by im- 
mersion in hot water. Volkens 1 2 states that a rootless plant 
of Mesembryan themum crystallinum continued to live for 
several weeks without any supply of water, and even pro- 
duced flowers : and the experience of growers of Cactaceae 
proves that rootless pieces of stem of Opuntia and other 
genera will throw out new branches in dry air. The cut- 
off rootless ends of shoots of E lode a canadensis may often 
be observed growing in the water, without any immediate 
root-formation having taken place. The extreme in this 
direction is reached by those plants which are rootless in the 
adult stage, the functions of the root being discharged by 
other organs : such plants are, among Vascular Cryptogams, 
Salvinia natans , Psilotum triquetrum , and possibly some 
Hymenophyllaceae such as Trichomanes emarginatum and 
the species of the genus Hemiphlebium 2 ; among Phanero- 
gams, Lemna arrhiza , Corallorhiza innata , Epipogium Gmelini , 
Tillandsia usnoides 3 , species of Ceratophyllum , all the species 
of Utricularia examined by Goebel 4 , and Aldrovanda 
vesiculosa . 
But these cases in which the morphological equilibrium 
between root and shoot is so considerably disturbed, are 
exceptions. The normal cases are those of chlorophyll- 
1 Loc. cit., p. 53. 
2 Prantl, Unters. zur Morphol. der Gefaesskryptogamen, I, pp. 29-31, 1875. 
3 Schimper, 1 . c., II, p. 68. 
4 Goebel, Flora, p. 291, 1889. 
