204 Barratt. — A Contribution to our Knowledge of the 
giving off aerial branches at nodes some distance away from the primary 
axis. 
In the later-sown cultures there was a tendency for an earlier prepara- 
tion for winter conditions. This is usually brought about by the formation 
of one or two tubers in the place of rhizomes (PI. VI, Fig. i, e,f)- 
In these artificial cultures it is well to bear in mind that the degree of 
development of the young plants is largely dependent on the external con- , 
ditions, and especially on the density of the culture. Plants closely crowded 
are correspondingly hampered and restricted in development. 
All the young plants figured in PI. VI, Fig. i, a-g , were taken from 
the same culture and were from prothallia of the same age. 
It is clear that the result of this early development of branches is the 
formation of a sympodium which is constructed from the bases of the first- 
formed aerial shoots. A distinct subterranean region is thus formed com- 
pounded from the bases of the second, third, and fourth aerial shoots. We 
shall see that the vascular structure of this region differs very strikingly 
both from the axis of the aerial stem and from that of the ordinary 
rhizomes. 
At the close of the first season’s growth the young plants may sho^ 
quite extensive branch systems. The primary and secondary axes 
generally die down early, and always before the end of the first season’s 
growth. 
Anatomy of the Sporeling. 
The primary root exhibits a simple diarch structure, each xylem strand 
being composed at first of a single series of tracheides. As the root 
approaches the region of the foot the xylem is increased by the addition of 
relatively wider but shorter tracheides with coarsely reticulate markings, 
strikingly different from the typical long spiral and annular elements of the 
root. The normal elongated elements thus give place to a more or less 
solid mass of short strongly thickened tracheides which are of the type so 
constantly met with in the nodal regions of the mature plant. 
Text-fig. i illustrates a series of transverse sections taken through 
a sporeling which has already produced a second aerial axis. From these 
it will be seen that the stele enlarges as it passes from the root upwards, 
and that the increase of tissue is due to the addition to the xylem of both 
parenchymatous cells and tracheides. One or two parenchymatous elements 
are found towards the centre of the mass (Text-fig. i, c), but at this stage 
they are neither numerous enough nor sufficiently constant in position to 
constitute a pith. 
Under a high magnification these tracheides often exhibit an unusual 
appearance when seen in transverse section ; the walls bordering on paren- 
chymatous cells are thin and unlignified, a condition which tends to over- 
