578 Fr. O. BOWER, 
tissue, which divides the central vascular group into two parts. 
As we pass further upwards, the variation from the true root type 
extends. In fig. vi, 2, we have a condition in which the proto- 
xylem masses, though they are still only two in number, are 
separated further from one another. This separation is due to 
an active increase in bulk of the parenchymatous tissue origi- 
nally lying between them. It will be noticed that the compo- 
nents of each group tend to arrange themselves radially around 
the protoxylem masses as centres. 
As we again pass further upwards, at a short distance above 
Section 2, each protoxylem mass is seen to divide into two (fig. 
vit, 3), and at the same time each of the two groups of bundles 
is divided by a plate of parenchyma into two, so that the central 
system of bundles now appears arranged in four groups. Hach 
of these includes one protoxylem mass, around which the other 
bundles of the group tend to arrange themselves radially. It 
will be noticed that the distance of the two pairs of protoxylem 
masses in 8 from one another is greater than that of the single 
mass in 2, while the whole section is elliptical in form. This is 
doubtless the result mainly of the secondary activity of the 
parenchyma so often alluded to. The number of peripheral 
bundles is increased. Referring to fig. 111, it will be seen that 
between the points 3 and 4 there occurs a sudden swelling of 
the stock, hence the difference in area between 3 and 4 of fig. v1. 
As they pursue their course upwards from 3, the four protoxylem 
masses, with the groups of bundles surrounding them, separate 
from one another till all four are at equal distances apart. 
Meanwhile the bundles of each of the groups arrange themselves 
nearly symmetrically round the four centres. The peripheral 
bundles undergo frequent anastomosis at the point of swelling, 
both with one another and with members of the four central 
groups. A comparison of the sections represented in figs. v1, 3 
and 4, shows that though the plant increases very largely in 
thickness between the planes of these two sections, still the vas- 
cular system does not become much stronger, but that the paren- 
chyma increases very much in bulk. (N.B.—The bundles in fig. 
vi, 4, are drawn rather too thick.) Here, then, we have to deal 
with a more prominent instance of the effect of the activity of the 
parenchyma. A comparison of fig. v1, 1—4, with fig. 15 eu 
and fig. 22 of my former paper will throw some light on the 
process of development. If allowance be made for the difference 
of scale of the two series, it will be seen that a great increase of 
bulk has taken place, and that in proportion to that increase in 
bulk the original protoxylem masses have become separated fur- 
ther from one another, i. ¢. that the increase is due not to a pro- 
cess of external apposition of tissues, as would be the case if the 
