304 PROF. F. О. BOWER ON APOSPORY AND ALLIED PHENOMENA. 
covering numerous small green or brownish sporangia. A microscopic observation of the 
sporangia will, however, disclose the fact that even at this period the oldest of them have 
already begun to assume abnormal characters. Transverse sections of a pinnule, so cut 
as to pass through a sorus, show that, in their early stages of development, the sporangia 
have that arrangement and succession of cell-divisions which is usual; each is thus seen 
to be an elongated, club-shaped body, consisting of a massive stalk and a head composed 
of a single central cell (the archespore), surrounded at first by a single layer of investing 
cells, which in the normal sporangium give rise to the outer wall and annulus (Plate LVII. 
figs. 1, 2). In the majority of cases the normal course of development is arrested at this 
stage, and the peculiarities to be described take their origin by purely vegetative growth 
from the cells of the young sporangium ; in other cases, however, the normal course of 
development of the sporangium may proceed further; thus in fig. Та Ше archespore has 
again divided as in normal sporangia, so as to form the first cell of the tapetum ; again, in 
other, but rare examples the annulus has been seen almost fully developed, and in one 
specimen even Ше spore-mother-cells were observed already separated. from one another, 
and lying freely within the enlarged cavity of the sporangium. This was, however, the 
most advanced specimen seen, and it may be stated plainly that, in the many observations 
made on material taken at various periods, not a single sporangium has been found to 
produce mature spores. The plant is, then, so far as experience goes, an example of 
complete sporal arrest. 
We may now proceed to the study of those abnormal developments which appear in 
this plant, and, as regards the propagation of the variety, take the place of the formation 
of spores. In all cases observed these consist, in the first place, in the growth and divi- 
sion of the cells of the young arrested sporangia, and of the sporangia only. The tissues 
thus produced are thin-walled, and even when they form solid masses (as is not unfre- 
quently the case) they exhibit no internal differentiation. The contents of the cells con- 
sist of plentiful protoplasm, with numerous chlorophyll granules, which, as development 
proceeds, elaborate considerable stores of starch (figs. 3, 4). This being the case, they are 
obviously self-supporting after the first stages are past, and this is clearly shown in cul- 
tures which have been grown for a few weeks under a bell-glass on moist soil ; in these, 
though the tissues of the parent frond die and turn brown, even up to the very stalk of 
the sporangia, the tissues of the latter present a green and healthy appearance. 
In some cases the vegetative growth and cell-division extend generally to all tissues of 
the sporangium ; in others it appears more specially localized in different parts of the 
sporangium, and this difference appears to depend upon the period of development which 
the sporangium had reached before the substitution of vegetative growth had interfered 
with the normal course of development. It may be stated, as a general result of very 
numerous observations, that the earlier the arrest of the normal development the more 
complete and generalis the substitution of the vegetative growth throughout the spo- 
rangium ; while conversely, in those sporangia in which the normal development has pro- 
ceeded furthest, either no substitutionary vegetative growth appears, or it is only to be 
found in the cells composing the stalk of the sporangium. "Taking the latter case first, in 
