672 
PROFESSOR F. O. BOWER ON THE DEVELOPMENT AND 
intercalary growth is more strong on the lower than on the upper side of the new 
tuber, the whole body of it becomes inverted, in a manner not unlike that already 
well known in the tubers of certain orchids.* Fig. 31 represents in general outline 
the form and position which are thus assumed by a developing tuber : the apex (a) 
still maintains an oblique position; above it is a small cavity, more clearly seen in the 
specimen drawn under a higher power in fig. 32 ; from this cavity the now closed 
channel, which originally communicated with the open air, may be traced upwards, as 
seen in figs. 31, 32, till on approaching the outer surface it again widens out as a 
funnel-like depression (shown in fig. 33), which may often be recognised even in the 
mature plant (fig. 26). It may further be noted that a vascular strand, already 
described as existing in the stalk of the mature tuber, runs down from the main body 
of the plant till it approaches the apex of the new tuber ; but, as above stated, it 
stops short before reaching the new apex. It may here be again remarked that 
among the plants grown at Kew no case has been observed of the formation of more 
than a single tuber: if this be uniformly the case with Pliylloglossum, there can be no 
increase in number of individuals by means of the tubers, and at present no other 
form of vegetative reproduction is known in this plant: this would lead us to expect 
that the plant depends for its multiplication upon the germination of its spores, and 
this will enhance the interest which attempts to raise the plant from spores would 
naturally arouse. 
If a median longitudinal section be cut through the conical outgrowth which 
ultimately develops as the root, while it is still young, its structure is seen to be 
such as is shown in fig. 34. It is clear from such preparations that there is no 
question of endogenous origin of the outgrowth, since the outer margin of the section 
is continuous, smooth, and unbroken from the surface of the axis, over the whole of 
the swelling. There can be no doubt that the whole outgrowth is of exogenous 
origin. The superficial cells are subject to both periclinal and anticlinal division, 
and consequently there is no clearly marked dermatogen ; this is the case for all the 
other organs of the plant while young. As the outgrowth increases in age and size, 
periclinal divisions, which may already be observed at the point of greatest convexity 
in fig. 34, become more frequent, and being repeated in the same cells, result 
ultimately in the formation of a root-cap, which may then be recognised externally 
as the slight excrescence at the apex, as above described ; the root-cap is thus 
derived in this case from superficial cells, and the whole root is of exogenous 
origin. In Pliylloglossum another plant is added to the list of those in which the 
root is described as being of exogenous origint: it is interesting to note that among 
them is Isoetes, in which the first root of the embryo is stated to originate from 
superficial cells. 
* Ikmisch. “ Biologie und Morpbologie der Orchideen.” Leipzig. 1853. 
f Compare Goebel. “ Vergleicliende Entwickelungsgeschichte,” p. 350. 
* Sapebeck. “ Gefasskiyptogamen,” p. 229. 
