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



A somewhat similar view, though different in some details, may be 

 held also in the case of Botrychium. 



There are, however, other facts relating to both the Ophioglossacese 

 and Lycopodinee which are obvious externally, and which are, I think, 

 most readily explained on an hypothesis of elaboration and partial 

 sterilisation : these will now be briefly alluded to. In certain species 

 of Lycopodium (e.g., L. Selago) there is no marked difference between 

 the foliage leaves and the sporophylls : in many other species the 

 difference is only slight. It may be noted that in certain species 

 (e.g., L. alpinum) towards the base of the strobilus the young 

 sporangia show gradual reduction in size, these leading on to cases of 

 complete abortion. At the apex of the strobilus also there is often a 

 similar reduction of the sporangia (Phylloglossum, L. clavatum, &c.), 

 the uppermost leaves being thus sterile. Again in L. Selago and 

 some tropical species, sporangia are borne on certain zones of .the 

 plant, while on alternating zones there are only sterile leaves. In the 

 Ophioglossaceae also the leaves of weak plants are frequently sterile, 

 and bear no matured " fertile fronds " : examination of these, how- 

 ever, frequently discloses a small and abortive " fertile frond " occu- 

 pying the position of the normal one. How are these organs in the 

 Lycopods and Ophioglossum to be explained unless they be regarded 

 as the reduced and abortive remains of parts, which under other 

 circumstances might have come to functional maturity ? They are, 

 in fact, evidence of further sterilisation, though in this case it is not 

 partial, but extends even to the whole sporogenous tissue of certain 

 sporangia. 



Putting together these last facts, and the developmental data pre- 

 viously stated, the following seems to me to be a reasonable theory, 

 which will, I think, throw some light upon the probable relations of 

 the Lycopodinae and Ophioglossaceas from the point of view of 

 descent : 



The primeval strobilus consisted of axis, sporophylls, and sporangia : 

 any of these parts was capable of further elaboration, and the balance 

 of them inter se might thus have been modified. 



In Phylloglossum there is a small strobilus which springs directly 

 from the protocorm. This whole strobilus is probably of a primitive 

 type, and may correspond to an elaborated sporogonial head (see below). 



In the various species of Lycopodium the whole plant (exclusive of 

 the protocorm, &c.) represents an extended and branched form of 

 such a strobilus, of which many of the sporophylls have been steril- 

 ised, and appear as the foliage leaves, having no sporangia. The 

 whole plant shows a prevalence of development of the axis over the 

 leaves or sporangia. 



In the Ophioglossaceae the converse is the case ; the axis remains 

 relatively small (except in Helminthostachys, where it is seen as the 



