THEIR CYTOLOGICAL DISTINCTION 61 



Nephrodium Filix Mas, as occurring on the leaf-bases (Fig. i), and in 

 Cystopteris bulbifei-a, at points on the upper region of the leaf (Fig. 3). 

 It also occurs in various forms in many other Ferns, in Lycopods, and 

 Equiseta. The essential feature of it is that a portion of tissue of the 

 sporophyte, developed as a bud with axis leaves and roots, on being 

 detached from the parent plant, may continue its growth apart from the 

 parent. This is plainly a mere vegetative amplification of the sporophyte 

 itself, and its tissues are at first continuous into those of the bud : there 

 is no reason to think that any nuclear change accompanies the production 

 of these growths, and the result is the establishment of physiologically 

 independent individuals ; but their origin and detachment do not modify 

 our conception of the sporophyte as a whole in any essential point. If 

 that conception be based upon nuclear changes accompanying fertilisation 

 and reduction, it will include all such results of vegetative amplification : 

 they will be held to be intra-sporophytic means of propagation. 



Similarly, in the case of gametophytic budding, which is common in 

 Liverworts, Mosses, and in certain Ferns, by means of gemmae : these 

 are small bodies, consisting of one or more cells, which are easily 

 detached and under suitable conditions develop into new gametophytes. 

 Here again the gemmae appear to be mere vegetative growths, and 

 they secure increase in number of physiologically independent individuals ; 

 but there is no reason to think that there is any nuclear disturbance 

 involved : they may be regarded as intra-gametophytic means of propagation. 



How, then, do the irregularities above described affect the general view 

 of the cytological distinction between the two alternating generations of the 

 Archegoniatae ? It is quite clear that an absolute chromosome-distinction 

 cannot be held as universally applicable at the present time to the two 

 alternating phases : nor does form depend on the exact number of the 

 chromosomes : nor yet is there any obligatory ratio according to which 

 the gametophyte is always haploid and the sporophyte always diploid. 

 These facts give an opening to the facile conclusion that the chromosome- 

 distinction is worthless, and opinions to this effect have already been 

 expressed. But the recognition of the present existence of aberrant forms 

 does not negative the importance of the relation which is usually seen, 

 nor exclude it from taking its due place in the reconstruction of the 

 history of the past. It is contrary to all evolutionary theory and 

 experience to assume that what has been normal in the past is 

 obligatory for the present or the future. Moreover, it seems probable 

 that these abnormalities do not represent anything which took a settled 

 place in the course of the evolution of the plants in which they appear : 

 our opinion might be different if in any of the great phyla it could be 

 shown that a definite stock, or line of descent, had been permanently 

 established showing aberrant characters ; for instance a permanent Arche- 

 goniate phylum showing a cycle without any chromosome-differences. But 

 of this there is no evidence at all : every one of the main phyla 



