Oliver —On Sar codes sanguined , Torr. 31 1 
that,, in Sarcodes , all lateral roots are formed exogenously and 
not from any internal pericycle as happens in ordinary cases. 
In Monotropa , on the other hand, the roots branch always 
normally, that is, endogenously. This was shown by Drude 1 
and by Kamienski 2 , and I have found it to be the case in all 
specimens examined. The only other genus of Monotropeae, 
the roots of which have been available for examination, is 
Pterospora . Here, not only is there a well-marked mycorhiza, 
but the root-branching is exogenous and agrees with Sarcodes. 
That these root-like organs in Sarcodes and Pterospora are 
true roots is not, I think, to be questioned. They possess 
well-marked root-caps, their bundles are radially arranged, and 
there is a total absence on them of scale-leaves of any kind. 
The exogenous branching of the roots, occurring in Sarcodes 
and Pterospora , may be regarded as a special adaptation, in 
these plants, that has been perpetuated as being a useful 
variation. By an exogenous method of root-branching the 
formation of a wound, which must always occur in endogenous 
branching, is avoided, and the inner tissues of the plant will 
not be so liable to the entry of the fungus forming the my- 
corhiza. In the case of endogenous branching the wounds 
formed in the cortex, by the penetration of the lateral roots, 
must be points of weakness should there be any tendency on 
the part of the fungus to make an entrance. It must be 
admitted that in Monotropa , where lateral roots arise endo- 
genously, no such behaviour of the fungal hyphae has been 
observed. However, before discarding the view above put 
forward it must be remembered that at present really very 
little is known of the nature of these mycorhiza-fungi, and 
whether the conditions that obtain in one case hold good for 
another. An alternative, and perhaps simpler, explanation of 
the phenomenon may be suggested by the general reduction 
of the vegetative organs, as a whole, in these saprophytic 
plants. The organs of plants which obtain most of their food 
in the form of complex organic substances show less histo- 
1 Drude, 1. c., p. 43, and PL III. Fig. 15. 
2 Kamienski, 1. c., p. 18, and PI. I. Fig. 8. 
