138 



Prof. F. 0. Bower. Studies in the 



[Dec. 5, 



of the anther is the ordinary quadrilocular type, but in certain genera * 

 transverse septa are formed in each of the four pollen-sacs by conver- 

 sion of certain cells of the potential archesporium into sterile tissue ; 

 the unavoidable conclusion already drawn by other writers for this 

 and other cases, is that these septate anthers are derived from those 

 of the ordinary quadrilocular type, and the process of septation thus 

 illustrated is essentially similar to that described for the Lycopodineaa 

 in my previous paper. We thus see that septation of sporangia has 

 actually occurred, and that it is a rather wide-spread phenomenon in 

 Angiosperms. It will therefore be merely a question of probability 

 whether, and how far, it has also occurred in lower forms, and whether 

 it is by septation that those synangia were produced, which are so 

 marked a feature in certain Pteridophyta. 



The argument from developmental evidence is comparatively 

 simple where, as in the Angiosperms, the meristems are distinctly 

 stratified, and the archesporium is a definite layer, ultimately hypo- 

 dermal in origin ; but in applying a similar argument to the 

 Pteridophyta, in which the meristems are not clearly stratified, it is 

 less easy to arrive at a conclusion. The principle is to be laid down 

 that the study of the sporangia or synangia of a plant is to be carried 

 out in the light of a knowledge of the segmentation of its apical meristems. 

 The sporangia are parts of the plant-body, and their segmentations 

 do not differ essentially from those of the meristems of the other 

 parts of the plants on which they occur. Where the meristems are 

 stratified, as in Angiosperms, a clearly stratified structure of the 

 sporangia is commonly found ; where, as in the Pteridophyta, the 

 meristems are not stratified, it would be plainly unreasonable to 

 expect a stratified structure of the sporangia, and such structure is 

 not found. Accordingly, in using developmental evidence in solving 

 the question whether synangia in Pteridophytes resulted from septa- 

 tion, the existence of a continuous hypodermal archesporium cannot 

 reasonably be demanded as evidence of septation, though of course it 

 may occur, as indeed it does in Isoetes ; it is, however, to be remem- 

 bered that in this plant the meristems are more clearly stratified than 

 in most Pteridophyta. 



The considerations thus briefly epitomised are a necessary prelude 

 to the comparative study of the Ophioglossaceae. In my preliminary 

 statement (' Roy. Soc. Proc.,' vol. 50, p. 265) I have described, chiefly 

 from examination of Ophioglossum pendulum, a continuous hypodermal 

 band as the potential archesporium, which subsequently was differ- 

 entiated into sporogenous groups and septa ; such a band appears 

 with some degree of regularity in this species, but it is not constant, 

 and is not found with any clearly defined outer limit in 0. vulgatum 

 or reticulatum ; thus far I admit the validity of Rostowzew's criticism 

 of my preliminary statement (" JBeitr. z. Kenntniss der Ophioglosseen. 



