58 Worsdell . — The Structure and Morphology of the * Ovule! 
or of those of the caulome, we surely dare not conclude that this organ 
exhibits within itself a fusion of those two categories ! for if, in this 
particular case, such a fusion actually exists, we ought occasionally to find 
here and there in other plants, normally or abnormally, true transitional 
forms between, say, stem and leaf, or leaf and root, &c. If the existence 
of these could be demonstrated it would, in the writer’s opinion, prove our 
morphological categories to be mere figments of the imagination ; but he 
has no hesitation in saying that he believes such transitions never will be 
demonstrated. 
Until within comparatively recent years it was usual to regard the 
categories as four in number, and as consisting of the caulome or stem, the 
phyllome or leaf, the trichome or hair, and the root. A few writers, 
however, have advocated the introduction of a fifth category, viz., that of 
the sporangium ; a discussion of the validity of this view will be afforded 
at the proper time and place in this thesis. 
The ovule , which forms the subject of the present paper, does so on 
the ground of its being one of those highly complex (as may be assumed 
from the evolutionary point of view), much modified structures whose mor- 
phological nature has on that account remained for so long a doubtful 
quantity and the cause of deep debate and argument on the part of many 
able investigators. It will be the writer’s present object to endeavour to 
afford a presentation of the various views on the subject held by many 
of the leading botanists of the century, leaving his readers to judge for 
themselves which of those views contains the fullest measure of the truth. 
The facts thus collected and presented in a concise and accessible form will 
also, he hopes, prove useful to the student and the teacher of morphology. 
At the outset let us consider the few, simple facts connected with the 
structure and position of the ovule as they are familiar to us to-day. The 
ovule is well known to appear in very various positions on the plant ; in 
the majority of cases it appears as an outgrowth from the margin of the 
carpel ; in other cases as a development from the inner surface of that 
organ, as in Butomus and Nelumbium ; in older types of plant, the writer 
would submit, as terminal to a carpel of radial symmetry of structure, as 
in the fossil Bennettites ; in some instances, as in Caryophyllaceae and 
Primulaceae, it is apparently a product of an upgrowing axile placenta; 
in yet others there are indications of its actually terminating the floral 
axis, as in Compositae 1 , Piperaceae, Najas , Polygonaceae, Taxus. The facts 
connected with the position of the ovule have had no small share in in- 
fluencing the decision of botanists as to its morphological nature. There 
have, indeed, been not a few who have placed their whole reliance on this 
set of data, constituting it the central pivot of their deductions. The 
ovule, whatever its position on the plant, consists, as a general rule, of 
1 But the ovule here is really lateral. 
