350 Groom . — On Thismia A sefoe ( Beccari ) 
In most saprophytes the hyphae of the endotrophic my- 
corhiza do not enter parts of the shoot which are not 
absorbing. This is presumably because the chemotropically 
active substance, if present at all, is only extremely dilute and 
rapidly consumed by the host. If this view be correct we 
might expect in Thismia that any mycorhizal hyphae entering 
the inflorescence-axis would assume the form of the sheath- 
hyphae. This is in fact the case, as was mentioned earlier in 
the paper. Further, in Fig. 3, it can be seen that, as the 
cortex of the thallus approaches continuity with the paren- 
chyma of the primordium of the inflorescence-axis, the 
hyphae in the limiting layer of the former assume the 
characters of the exocortical hyphae : and the hyphae in 
the exocortex become straight. Employing a high-power 
objective it could be further seen that at the base of this 
primordium of the bud, in the cells continuous with the 
mediocortex, the hyphal-bladders' became fewer and the 
hyphae more uniform. These facts, I think, dismiss the 
suggestion which might be made, that the different behaviour 
of the hyphae in the various layers of the thallus is due, not 
to any distinction in the metabolism of the cells, but to the 
circumstance that, as the hyphae penetrate the deeper tissues, 
they may become more irritable to chemotropic stimuli. 
Physiological Significance of Endotrophic Mycorhiza. 
The precise source of the foods of guest and host in myco- 
rhiza has hitherto not been ascertained, neither has proof been 
given of any reciprocal interchange of nutritive substances 
between the two. The large dimensions of the hyphae in 
Thismia and their feeble branching in a cell rendered them 
peculiarly suited for such observations. Hence some com- 
ments on the physiological significance of mycorhiza may be 
of interest, particularly as the conclusions drawn differ con- 
siderably from those taught by Frank, who has recently 
devoted much attention to the subject. 
Frank gives two entirely different interpretations of the 
significance of the two forms of mycorhiza — ectotrophic and 
