258 



Prof. F. 0. Bower. Studies in the 



[Jan. 30 



ridge of some sharpness between the places is to create a distinct 

 shadow, to such an extent that the effect would be inappreciable ; the 

 same result would be produced by an intervening headland ; this 

 agrees with the experience of Captain Jackson.* 



" Studies in the Morphology of Spore-producing Members. — No. V. 

 General Comparisons, and Conclusion." By F. 0. Bower, 

 Sc.D., F.B.S., Eegius Professor of Botany in the University of 

 Glasgow. Eeceived January 30, — Read February 12, 1903. 



(Abstract.) 



This concluding Memoir contains a general discussion of the results 

 acquired in the four previous parts of this series, and of their bearing 

 on a theory of sterilisation in the sporophyte. The attempt is made 

 to build up the comparative morphology of the sporophyte from 

 below, by the study of its simpler types ; the higher and more 

 specialised types are left out of account, except for occasional com- 

 parison. It is assumed for the purposes of the discussion that alter- 

 nation of generations in the Archegoniatse is of the antithetic type, 

 and that apogamy and apospory are abnormalities, not of primary 

 origin. 



After a brief allusion to facts of sterilisation in the Sporogonia of 

 Bryophytes, the similar facts are summarised for the Pteridophytes. 

 It has been found that examples of sterilisation of potentially sporo- 

 genous cells are common also in vascular plants, while occasionally 

 cells which are normally sterile may develop spores. Hence it is 

 concluded that spore-production in the Archegoniate plants is not in 

 all cases strictly limited to, or denned by, preordained formative cells, 

 or cell-groups. A discussion of the archesporium follows, and though 

 it is found that in all Pteridophyta the sporogenous tissue is ultimately 

 referable to the segmentation of a superficial cell, or cells, still in 

 them, and indeed in vascular plants at large, the segmentations which 

 lead up to the formation of spore-mother-cells are not comparable in 

 all cases ; in fact, that there is no general law of segmentation under- 

 lying the existence of that cell or cells which a last analysis may 

 mark out as the " archesporium nor do these ultimate parent cells 

 give rise in all cases to cognate products. Therefore it is concluded 

 that the general application of a definite term to those ultimate j^arent 

 cells which the analysis discloses has no scientific meaning, beyond the 

 statement of the histiogenic fact. 



Further, it is shown that the tapetum is not a morphological constant, 



* ' Boy. See. Proc.,' 1902. 



