Op hi agios sum (C heir agios set) palmatum , Z. 297 
analysis to decide the method by which it is brought about. It will then 
appear that more than one method may be involved in any given example. 
For instance, where one primordium is already initiated, and the activity of 
tissue-formation becomes localized at more than one centre in relation to it, 
thus producing more than one part in place of the original one, the method 
of the pleiogeny would be chorisis. But if two centres of activity originate 
apart from one another where usually only one exists, or if an additional 
one appeared in a position usually untenanted, that would be interpolation. 
But both would fall under the general expression of pleiogeny. 
DESCRIPTION OF FIGURES IN PLATES XXII-XXIV. 
Illustrating Prof. Bower’s paper on Ophioglossum palmatum. 
Fig. r. a, Fertile plant of Ophioglossum palmatum represented complete, about three-quarters ot 
the natural size, from a drawing by Dr. A. A. Lawson. B, A bud inserted upon its parent root, 
showing the tuberous stock (t), surmounted by a dense tuft of hairs (h), and a single young 
leaf, x 2|. 
Fig. 2, I-IX. Successive transverse sections of a leaf-base, following the leaf-trace strands 
downwards to their insertion on the stele. I and II show the very numerous small strands, forming 
a more or less circular series, with frequent signs of fusion across the adaxial face of the petiole. 
Ill and IV show stages of segregation of the strands into two lateral groups, which in V and VI 
have united into single strands. V-X show the successive stages of insertion ot these, right and 
left, at points widely apart upon the margins of a leaf-gap. In V-VII a commissure of the vascular 
network is seen just above the leaf-gap, and from the middle of it arises a root ( rt ), which takes its 
course obliquely outwards (VII-IX). The leaf-trace strands do not fuse completely with the 
meristeles of the axis till the level of the gap is reached (VIII, IX). x about 6. 
Fig. 3. Photograph of a transverse section through the old stock, about half-way down its 
length, showing centrally the pith surrounded by three meristeles. From the edges of two of these 
a leaf-trace is coming off, as in Fig. 2, VIII. Externally numerous leaf-traces in various stages of 
advance are traversing the bulky cortex, and several roots are also seen, x 4. 
Fig. 4. A slightly diagrammatized key to the vascular system shown in Fig. 3. The roots are 
omitted for clearness, while the several foliar traces are connected by dotted lines and numbered. 
It will be seen that they conform to the stages shown in Fig. 2 ; also that the divergence between 
the successive leaves is not a constant one. 
Fig. 5, I-VII. Successive transverse sections of the stock of a young adventitious bud. I shows 
the insertion on the vascular system of the parent root ; II, the vascular ring surrounding the central 
pith, which is present from the first. In III the ring opens, but no leaf-trace was given off from 
the gap. In IV the ring has opened on the opposite side also, while each vascular meristele is 
giving off a root-trace. The first leaf-trace is shown coming off in V, as two separate strands from 
the edges of the second gap. In VI the strands are separated, but the first gap has closed again by 
a vascular commissure. In VII the second gap has also closed, reconstituting the ring, while the 
strands of the trace are diverging widely. Drawn freehand, x about 50. 
Fig. 6. Photograph of a transverse section of the old stock near to its base, showing the pith 
greatly dilated, the meristeles separated, and stretched transversely, while four roots are traversing 
the pith ; others are seen in the cortex, x 4. 
