260 Prof. F. 0. Bower. Studies in the [Dec. 17,. 



internal mass of spores. The higher Bryophyta show a larger pro- 

 portion of sterile tissue, which in them composes the seta, columella, 

 and wall, while the sporogenous tissue is comparatively reduced in 

 bulk, though still forming one united band. In the vascular plants 

 the proportion of sterile tissue to the sporogenous tissue is larger 

 still ; elaboration of form has in them resulted in the production of 

 appendicular organs, while the sporogenous tissue is partitioned off 

 into small, isolated masses, or even single cells, these being situated 

 in members which are commonly called sporangia. The series from 

 the lowest to the highest of these types probably illustrates the 

 essential points in the actual process of evolution of the higher from 

 the lower forms; from it we recognise that the ascending series 

 shows a progressive sterilisation of the tissues of the neutral genera- 

 tion, and also an increasing elaboration of external form and internal 

 structure, the two lines of progress going, in a measure, hand in hand. 



It is obvious that, if the progression were as above stated, the 

 function of the spore-production preceded the vegetative functions 

 of the sporophyte in point of time ; spore-producing members may, 

 in this sense, be termed primary from the point of view of descent, and 

 the vegetative members, secondary ; the morphology of spore-pro- 

 ducing members should accordingly take precedence of the morpho- 

 logy of vegetative members, and an exhaustive study of the former 

 is therefore specially necessary. 



The widest gap in the series of those plants which show antithetic 

 alternation is believed to be that between the Bryophytaand the Vas- 

 cular Cryptogams ; to bridge over this gap between plants with 

 simple form and united archesporium, and those with complex form 

 and separate small archesporia, is the most clearly outstanding prob- 

 lem of morphology. Of intermediate forms there are practically none 

 known ; but it is believed by the author that a careful examination 

 of the spore-producing members of the lower vascular plants, with 

 special regard to their development, will best lead to some clear 

 opinion as to the way in which the transition may have taken place. 

 A comparison of such plants as form natural series may demonstrate 

 progressions of elaboration and sterilisation, which may be regarded 

 as analogous to the progression from the Bryophyta to the Vascular 

 Cryptogams. Such an analogous progression is believed to be found 

 in the Lycopodina3 and Ophioglossacese. Even if this analogy be not 

 admitted, the further investigation of the sporangia of certain rarer 

 and less known Vascular Cryptogams, to be described below, will be 

 of sufficient interest to justify the work. 



The present preliminary statement will refer to the Lycopodinae 

 and Ophioglossaceae only. 



The simplest known type of the former is Phylloglossum, which I 

 agree with Dr. Treub in regarding as a truly rudimentary form. 



