EM PROF. F. O. BOWER ON APOSPORY AND ALLIED PHENOMENA. 
even when the more mature part is an almost perfect cylinder, the apical cone itself is 
flattened. Investigation of its structure has not disclosed the presence of any single 
initial cell; the arrangement is rather similar to that of a normal thallus after the first 
stages of development are past, the apical growth being conducted by a series of mar- 
ginal initial cells. Comparing these prothalloid growths, such as in fig. 27, with normal 
prothalli, they might perhaps be described as consisting of a massive cushion, without 
any development of wings. This conclusion is further borne out by the distribution of 
sexual organs upon them. — Antheridia have not been observed on any specimen of the 
type (B) ; on the other hand, archegonia are constantly present in large numbers, and 
that not only on the side which happens to be directed down wards, but almost in uniform 
distribution all round. "The archegonia themselves are to be found in all stages of deve- 
lopment, up to the period of decay; but as yet, on the cultures at Kew, no embryo plants 
have been observed. Subsequently to the appearance of the archegonia, the apical cone 
assumes a different character of development. Lateral wings are formed, and a flattened 
expansion is the result, with glandular marginal hairs and other characteristics of a 
normal prothallus ; but even on this, antheridia have not yet been found. Ап examina- 
tion of numerous prothalloid growths of the type (B) leads to the conclusion that they 
produce exclusively female organs. 
Though the types above described as (A) and (B) differ in their origin, in their 
external form, and also in their sexual characters, neither type is exclusively to be found 
on any one frond, pinna, or pinnule; it appears rather that any pinnule or sezment of a 
pinnule may assume either one or the other of these types of development. Further, an 
instance has been observed of both types of development being assumed by the same 
segment of a pinnule: this has been represented in fig. 30, where it will be recognized 
that not only has the extreme apex of the pinnule grown out into a flattened expansion 
(prth. A), but there is also a massive outgrowth from the surface resembling in position 
and other characters a prothalloid growth of the type (B) (prth. В). 
Turning now to those prothalloid growths which arise in connection with the sorus, 
and accordingly fall under our second head, it may be noted that the discovery of these 
is entirely subsequent to the publication of the preliminary notice in the Journ. Linn. 
Soc., Bot. vol. xxi. In the specimens received from Mr. Wollaston in August 1886, 
though the sori were composed of arrested sporangia, covered by a normal indusium, no 
further peculiarities were to be noted. Cultivation on moist soil for two or three months, 
at the normal temperature, but with sufficient protection from frost, resulted in the 
formation of prothalloid structures in connection with the sori themselves, and quite 
distinct from the outgrowths from the tips of the pinnules as above described; further, 
an examination of the figures (31-36) will suffice to show that these outgrowths are of 
vegetative origin, and do not arise from the germination of spores. 
Under this second head two types of development may be recognized, though they 
merge into one another: type (C), in which the origin of the prothalloid growth is from 
tne arrested sporangium, and type (D), in which the outgrowth is derived from the 
massive base of the sorus, or even in some cases apparently from the indusium. The 
microscopic examination of preparations of sori, after cultivation for two or three months, 
