56 ALTERNATING GENERATIONS 
but Dr. Lang’s drawing shows how, nevertheless, the prothalli in turn 
hasten to a fresh apogamy (Fig. 38), thus the two transitions may be 
repeated at near intervals of time. The same was seen to be the case 
in. Zrichomanes alatum, in which apospory and apogamy were found to 
succeed one another,! and it has recently been proved to hold also for 
Athyrium filix foemina, var. clarissima, Jones, and other Ferns.? 
Lastly, Goebel has shown? that when the seedling leaves of certain 
ferns are removed and cultivated on a moist substratum, aposporous 
growths may be induced, which show sometimes the most intimate inter- 
mixture of characters of the sporophyte and 
a the gametophyte. These developments appear 
to be similar in kind, though not in detail, to 
those described by Lang and others. It would 
doubtless be possible to erect upon such facts 
a superstructure of theory; but it is necessary 
to remember that by the abscision of a young 
part it is placed in an anomalous and extreme 
physiological position. It is improbable that 
such circumstances ever arose in the course 
of descent: and accordingly it must remain 
a quite open question what bearing, if any, 
such observations have upon the evolutionary 
story. They demonstrate possibilities: but 
possibilities are not the equivalent of historical 
data. 
The rapid succession of the transitions 
thus actually seen in some Ferns from the 
gta (Cropp). “Drawing by Dr: La esporophyte to the gametophyte, and the con- 
prothallus to sporophyte, and subse- VETS€, give some colour to the suggestion 
eee ee ttricg = made by Goebel, that the sporophytic buds 
he found in the deep-water specimens of 
fsoetes are to be viewed as extreme cases of the telescoping of the 
alternate generations. This state of affairs is very nearly matched by 
certain Adzantums observed by Lang, in which numerous sporophytic buds 
were produced from the sorus. Examination showed that they sprang in 
certain cases from the sporangia themselves, but not from the sporogenous 
tissue. If we imagine the gametophyte stage reduced in such cases, not 
to a very short phase only, as it is in Lang’s Nephrodium, but to the 
vanishing point, the result might be as in Goebel’s J/svezes. But we may 
Fic. 38. 
1 Ann. of Bot., vol. i., p. 269. 
2 Farmer and Digby, Anz. of Bot., 1907, p. 163-167. 
8 Sits. d. Math.-phys., Klasse d. K. Bayer. Akad. d. Wiss., xxxvii., 1907. Heft. ii., 
p- 119. This is interesting for comparison with my own negative. results on leaves of 
mature plants recorded in Azwn. of Bot., iv., p. 168 (1889). 
4 Bot. Zeit., 1879, p. I. 
