4 Tans ley and Chick . — Notes on the 
stem and thus comparable with the primary root" in Pterido- 
phytes. 
It is to Haberlandt’s admirable work on the Anatomy 
and Physiology of the Mosses that we owe the great bulk of 
our knowledge on this subject. He not only discovered 
most of the important facts but gave them a clear interpreta- 
tion in the light of evolutionary theory. The following 
notes are intended to supplement his work, both in the 
further elucidation of points in the histology of Bryophytic 
conducting systems, and in the discussion of the various evolu- 
tionary problems involved. 
I. The Conducting Strands of Liverworts. 
The great majority of Liverworts, as is well known, have 
no differentiated water-conducting tissues. Living, as many 
of them do, in constantly damp situations, or flourishing only 
during the season when they are surrounded by air with 
a very high relative humidity, and frequently covered with 
rain or dew, they are used to absorbing water over their 
whole surface. A certain number no doubt depend for 
their water supply, at least at certain periods, on what is 
absorbed through the rhizoids which fix the thallus to the 
substratum, but the whole of the under-surface is commonly 
provided with these rhizoids, and the entire body is seldom 
too large to admit of the ready conduction of the water so 
absorbed through the ordinary parenchyma-cells to every 
part of the plant. 
In a certain number of cases, however, among the thalloid 
forms, either assimilating parts of the thallus (P 'allavicinia, 
Symphyogyna , Hymenophyton ), or specialized reproductive 
branches (Marchantiaceae), are raised considerably above the 
substratum, and then special means are often adopted to 
facilitate the conduction of water to these remote parts. 
It is not our intention to review the various adaptations in 
question, but rather to confine ourselves to the ^consideration 
of one of them — the differentiation of a definite conducting 
strand. 
