PROF. F. О. BOWER ON APOSPORY AND ALLIED PHENOMENA. 315 
account of this sporal arrest, it is found that the cells composing the walls of the 
sporangia are without spiral thickening, and that the sporangia remain permanently 
closed; further, that the spores themselves, which appear colourless and transparent in 
the sporangia, are about one fifth to one tenth the size of the normal spores, while the 
elaters are entirely absent* ; this arrrest is, however, not quite constant, since in speci- 
mens of the plant from Lapland normal spores with elaters were not uncommonly to 
be found ; these observations have been made over a period of 20 years, and on material 
from many localities ; thus the phenomenon is of some constancy. No attempts to ger- 
minate the spores are on record; writers on the subject appear to assume that germina- 
tion does not take place. While regarding this as a case of sporal arrest, it is to be 
remembered that the Hguwiseta are well adapted to vegetative propagation, though in 
Е. litorale there is but occasionally a very slight unusual adaptation for this, to com- 
pensate for the apparent loss of function of the spores. Thus Е. litorale appears to be an 
example of sporal arrest, pure and simple, and often without any substitutionary growth. 
The case of Ше homosporous Lycopodiacez might also be mentioned: though the 
spores appear normally developed, the difficulty of germinating them is well known, and 
Treub + has recently expressed the opinion that the formation of prothalli directly from 
the spores is the exception rather than the rule; thus, though this can hardly be included 
under “ sporal arrest," the function of the spore seems rarely to be fulfilled, and biologi- 
cally the result is very similar to that in Æ. litorale. 
Among the Sphagna ате to be found examples of what may be termed а “ partial 
arrest." W. P. Schimper | describes and figures two kinds of spores as occurring either 
together in the same or in different capsules; the larger ones (Makrosporen) are capable 
of germination; the smaller, resulting apparently from the division of the mother-cells 
into 16 instead of 2 cells, have a diameter about one third that of the larger ones; and 
it is stated that they do not germinate (2. с. p. 11). Though the existence of these 
smaller spores has recently been confirmed, this statement as to their lacking the power of 
germination has been neither confirmed nor contradicted $. If they be really functionless, 
we have, in those cases where they occur in special capsules, a complete arrest as regards 
those individual plants ||; where they occur together with the large spores we may recog- 
nize this as partial arrest, a phenomenon which is of frequent occurrence in Hetero- 
sporous plants. : 
Passing now to the plants last named, in the formation of the microspores the full 
number of those initiated come, under normal circumstances, to maturity ; in the case of 
the macrospores, however, the full development of the few is at the expense of the many ; 
a greater or less number of the spores initiated are usually arrested at an early stage, and 
do not come to functional maturity; it will be sufficient to cite such well-known 
+ Г, c. Taf. xviii. fig. 24. 
+ Ann. Jard. Bot. Buitenzorg, vol. v. p. 88. | 
+ Entwickelungsgeschichte der Torfmoose, 1858, р. 31, Taf. xi. figs. 16-20. 
§ Warnstorf, * Hedwigia, 1886, p. 89. : 
|| Warnstorf states (1. c. p. 91) that the small capsules most frequently occur on special plants. 
