60 ALTERNATING GENERATIONS 
budding. But an exact parallel is found in Athyrium filix-foemina, var. 
clarissima, Bolton, and in Scolopendrium vulgare, var. crispum Drummondae, 
in which the embryo arises from the unfertilised ovum.1 It may be 
remarked that the phenomena thus seen in the last-named Ferns and in 
Marsilia correspond essentially to what has been described for certain 
Phanerogams.? It thus appears that in a number of cases, systematically 
apart from one another, a diploid condition of the gametophyte is associated 
with apogamous development from a diploid unfertilised ovum: the 
abnormality is initiated by omission of the reduction in the spore-mother- 
cell, and consequently the diploid state is continued in the gametophyte, 
which -is normally haploid. It is important to note in such cases that 
a double number of chromosomes may be present without producing 
fundamental change of form or of external character in the gametophyte. 
The further question will then present itself, whether under any 
circumstances the converse is possible, or has been observed, viz. that 
the phase normally diploid, that is, the sporophyte, may be haploid? 
Strasburger states (/c, p. 166) that no case has come under his 
observation in which the generation normally diploid has only the reduced 
number of chromosomes. No case of a haploid sporophyte has yet been 
proved beyond doubt; but a reasonable probability has been established 
by Farmer and Miss Digby in the case of Lastraea pseudo-mas, var. 
cristata, Druery (2c, p. 180). The detached leaf of this plant produces 
prothalli from its margin or surface, which bear occasional antheridia, 
but the sporophyte is apogamous. The chromosome-number in the 
prothallus is about 60: in the embryo the number varies considerably, 
one mean being 60, another mean number being about 78. No migration 
of nuclei was observed, nor is there any reduction in the whole cycle. 
The relatively small number of chromosomes in the nuclei of the sporophyte 
is striking, and suggested to Farmer and Miss Digby that the gametophyte 
character had been impressed on the sporophyte—the converse, in fact, of 
what was seen in the varieties of Athyrivm and in Marsiia. A comparison 
of the chromosome-number (60, 78) with that in normal Las¢raea 
pseudo-mas (144) certainly indicates that this is the probable condition 
of the apogamous sporophyte of Druery’s variety: that the sporophyte is 
irregularly haploid, and that the whole cycle is essentially haploid 
throughout.’ 
It still remains to refer briefly to two other modifications of the normal 
cycle of alternation in Archegoniate Plants, so as to complete the tale of 
those which have been observed: I mean sporophytic and gametophytic 
budding. The - former has already been mentioned in the case of 
1¥Farmer and Digby, /c., p. 171. 
2 Fu-alchemilla, ‘Thalictrum, Antennaria, Taraxacum. See Strasburger, Zc., p. 139. 
’The examples quoted illustrate the more important modifications of the chromosome- 
cycle hitherto described. For further details reference must be made to the papers from 
which these have been derived. 
