1030 REPORT— 1898. 



steps between tliem. This condition in a plant, which on general grounds of com- 

 parison we believe to be primitive, is certainly interesting, and we shall ask 

 whether the two types of leaf have not arisen by distinct evolutionary sequence ? 

 In the genus Lycopodium there are certain species, such as L. Sclar/o, which show 

 alternately sterile and fertile zones ; examining the limits of the sterile zones, we 

 find at the base of each leaf an atrophied sporangium, similar in position to that 

 borne by a sporophyll. Wlien we compare this condition with that of Phylloglossum 

 it appears probable that tlio successive zones are the result of a metamorphosis of 

 a strobilus, which had a continuous apical growth, and unlimited repetition of 

 sporophylls, but that some of these suffered atrophy of their sporangia, with the 

 correlative effect of a larger vegetative development. A diti'erentiation of the 

 strobilus thus results in the plant as we see it, a production of foliage leaves by 

 sterilisation of sporophylls. Recognising this, some may suggest that the proto- 

 phylls originated in the same way. It is possible that they did ; but it is equally 

 possible, and, in view of the peculiar case of Phi/Uofflossian, I think more probable, 

 that in these plants we have an example of homoplastic development of parts dis- 

 tinct as to descent, while the limits of the two still evident in Phylloglosmm 

 became obliterated in the more complex case of Lycopodium. The proof of the point 

 will be difficult or even impossible, but the eyes of botanists should certainly be 

 open to recognise such individual homoplasy, should it occur, and to inquire 

 whether it has really had a place in plant-development. 



Returning now to homoplastic development in distinct groups of plants, the 

 morphology of the/oo< provides interesting material for comparison, and especially 

 so since there is no question of repetition here ; for the comparison is between 

 parts of which only one appears on each individual plant. 



The term foot has been applied to that part of the embryo in Pteridophyta 

 which serves to connect it physiologically with the prothallus \ the term has also 

 been used for the base of the seta in Bryophytes. Parts performing a similar 

 function, but not referable as in other Phanerogams to the metamorphosis of 

 cotyledons, are also found in Gnetum and Welwitschia. 



In the Bryophyta what is usually called the foot is no deBnitely specialised 

 structure ; it is merely the absorbent base of the seta. It would appear probable 

 that in the Bryophyta a true homogeny holds in all cases, as the requirement for it 

 will have been uniform ; and its basal position is also uniform, though some differ- 

 ence of detail does appear in the relation of this absorbing body to the first segmen- 

 tations of the embryo. 



In the Pteridophyta it is exceedingly difficult to be sure of the correspondence by 

 descent of the foot in distinct types, and indeed it should not be assumed that a 

 specialised absorbent organ was always present, though general surface-absorption 

 will naturally have taken place in all archegouiate embryos ; indeed, the condition 

 of some upright embryos is such that a foot would never have been described, 

 were it not for comparison with other types. In Eqtiisetum, Isoetes, Botrychium 

 — all forms without a suspensor, and with an upright growing embryo — the hypo- 

 basal half of the embryo, with or without a root, is absorbent as in the Bryo- 

 phyta, and is described as a foot ; it is quite possible to see in them the continuation 

 of a primitive absorbent organ. This may also be the case in the Marattiacete, 

 and it is specially noted by Campbell that' in Marattia all the superficial cells of 

 the central region become enlarged and act as absorbent cells for the nourishment 

 of the embryo.' From such types we may imagine the more specialised foot of the 

 Leptosporaugiate Ferns to have been derived by a localisation of the absorbent 

 function on one side only, which would be a natural consequence of the embryo 

 taking the prone, in place of the vertical position. 



A different course of events probably occurred in the Lycopodinese. I am 

 disposed to think that here the suspensor represents nothing more than a specialised 

 part of the primitive absorbent organ ; this seems to be indicated by the details as 

 shown in Treub's figures of L. cenmum and L. Fhlegmaria, in which the suspensor 

 is continuous with the foot. But what is, then, the ' foot' of Selayindla, which is 

 quite apart from the suspensor, the root intervenina: ? On this point I think we 

 obtain light from Welwitschia and Gnetum, for in these we see an absorptive 



