362 Take da. -—A Theory of ■ Transfusion-tissue'. 
Correlating these facts, we have very little difficulty in regarding 
the ‘ transfusion-tissue ’ as a tracheidal water-storing tissue, the elements 
of which may well be called water-tracheides, as generally termed. 
Then we can duly perceive that the so-called f accessory transfusion- 
tissue ’ occurring in the leaves of Cycads, Ginkgo , and of broad-leaved 
Podocarps is a real auxiliary conducting system, transmitting water from 
the vascular bundle towards the margin of the leaf, though of course it is 
quite evident that this tissue is derived from mesophyll-parenchyma. 
The tracheidal water-storing tissue occurs not only in the ordinary 
leaves, but also in the bracts and cone-scales (mostly of female cones) of 
the Gymnosperms, where storing water is necessitated . 1 
Not only in recent plants, but also in some fossil Gymnosperms and 
Lycopods, the ‘transfusion-tissue’ has been described . 2 In these plants 
the tissue in question occurs just as it does in W elwitschia, surrounding 
vascular bundles and being more or less separated from the latter. It 
appears to me highly probable that this tissue here also served as a water- 
reservoir, as it does in the recent plants. 
In the foregoing pages I have endeavoured to show the origin and 
function of the ‘ transfusion-tissue ’, and now it is quite clear that the tissue 
in question is not a modification of the centripetal xylem, nor is it an 
auxiliary conducting system, but it is a special sort of water-reservoir derived 
from pericyclic as well as mesophyll parenchyma. 
Summary. 
The orthodox ‘ transfusion-tissue ’ always arises laterally, and generally 
from the pericyclic region of the vascular bundle, quite independent of the 
centripetal xylem. Mesophyll-parenchyma often takes a share. Therefore, 
it is not a vestige of the centripetal xylem and is not to be reckoned as of 
phylogenetic importance. 
Its function is water-storing. 
The so-called ‘ accessory transfusion-tissue ’ serves to transmit water 
from the vascular bundle towards the margin of the leaf, and this is, as is 
well known, derived from mesophyll-parenchyma. 
1 The water-storing tissue in the bracts and scales of the Conifers has been thoroughly 
investigated by Bernard (2), who calls this tissue ‘ le bois centripete’. It is quite obvious that these 
parts of plants require water, as we see in the husk of the common hazel. 
2 A general account of this is found in Scott (10) ; also a description of the ‘ transfusion-tissue ’ 
in Prepinus , & c., is given by Jeffrey (6). 
