1394 A TEXTBOOK OF THEORETICAL BOTANY 



anatropous ovule is prolonged into a curly appendage which is twice 

 as long as the ovule. Nartheciiim (Liliaceae) has anatropous ovules which 

 are attached to the middle of a straight column, of which the lower part forms 

 the funicle and the upper part is an outgrowth from the chalaza. 



Such chalazal outgrowths are not uncommon in the Bromeliaceae. They 

 are sometimes classified as arils and as they become flattened and mem- 

 branous in the ripe seed, they aid its dispersal by wind. 



The morphological interpretation of the ovule has long been a contro- 

 versial question and it is clearly not one which can be considered only in 

 relation to the Angiosperms, for the Gymnosperms and the Pteridosperms 

 must also be taken into account. 



Three opposed theories have long been in the field and each has obtained 

 numerous supporters. 



1. The Axial Theory. The nucellus is a bud, i.e., a contracted axis, 

 and the integuments are its lateral foliar appendages. 



2. The Foliolar Theory. The ovule belongs to the category of phyllome. 

 The nucellus is an emergence on the upper surface of a carpellary 

 leaflet and the integuments are fused lateral lobes of the same seg- 

 ment of the megasporophyll. 



3. The Sui Generis Theory. The ovule is an independent structure, 

 borne either on axial or foliar organs, and the integuments are new 

 formations. 



The debate about these theories was formerly centred on the angio- 

 spermic ovule and the foliar nature of the carpel was accepted almost with- 

 out question as a basis of argument. Thus, if the first theory were correct, 

 then ovules, being buds, could not be borne directly on foliar carpels. As 

 ovules are, in fact, often attached to carpels, it had to be maintained that the 

 placenta was axial and that its fusion to the carpellary wall gave rise to the 

 appearance of attachment to the carpels. If, on the other hand, the second 

 theory were correct, then how could one account for basal ovules or those on 

 free-central placentae, which appeared to be direct continuations of the 

 floral receptacle? Moreover the second theory made the ovule a part of the 

 carpel and this led its more extreme supporters to deny that the female 

 reproductive organs of Gymnosperms and Pteridosperms are ovules, since 

 without carpels, they could not be so. As Celakovsky said, " no ovule 

 without a carpel ", an opinion indefensible at the present day. 



The inconsistencies and the strained interpretations which resulted 

 from the exclusive application of either theory led many morphologists to 

 the conclusion that ovules might be of both kinds and the question whether 

 in particular cases the ovules are cauline or foliar may still be found in 

 textbooks in current use. The corollary, that this state of affairs might 

 imply different lines of evolutionary descent for even closely related Angio- 

 sperms, did not obtrude itself. 



Increasing knowledge of the Gymnosperms and, still more, of the Pteri- 

 dosperms has led modern attempts to solve the problem away from the 



