An Historical Sketch. 
59 
three distinct parts : a central structure, the nucellus , which assumes a 
terminal position on the ovular rudiment, and two integuments , which onto- 
genetically arise as annular outgrowths from the basal portion of that 
structure ; the order of development of these integuments is basipetal, the 
inner, as regards the great majority of cases, preceding the outer (Fig. i). 
To these facts of the normal structure a few exceptions occur : the integu- 
ment may be entirely absent, as in Crinum ; there may be only a single 
integument present, as in Ranunculaceae, Piperaceae, and apparently also 
in the group of the Gamopetalae 1 ; on the other hand, the number of 
integuments may be increased, for C. Schimper is said to have found three 
in Reseda lutea , the third integument arising in the acropetal direction, i. e. 
within the two normal ones ; such a case as this latter, however, requires 
confirmation. 
In the present thesis the writer is purposely omitting any reference 
to the nature of the ovule in parasitic plants, as he hopes to treat this 
subject separately on some future occasion. 
The facts of the normally constructed ovule being given, viz., a central 
papilla, the nucellus, enveloped by two basipetally-developed integuments, 
the problem which both past and present botanists have set themselves 
to solve is this: to which of the morphological categories does this im- 
portant structure belong? 
The views which have been held on this subject may be classified 
i 
Fig. i. Fig. 2. Fig. 3. 
Fig. 1. Diagrammatic representation of the ovule to illustrate the actual structure apart from 
its morphological interpretation. Fig. 2. Diagrammatic representation of the ovule to illustrate 
its interpretation according to the axial-theory (after £elakovsky). Fig. 3. Diagrammatic 
representation of the ovule to illustrate its interpretation according to the foliolar theory (after 
telakovsky). n, nucellus ; i. int ., inner integument ; 0 . int., outer integument. 
under three main headings, according as the ovule has been held to possess 
the morphological value of: — 
1 . a shoot ; 
2. a leaflet ; 
3. a new structure or sporangium. 
1 In this group of plants, at any rate, the * single ’ integument is probably due to congenital 
fusion of the two integuments. 
