204 SYMMETRY OF THE SPOROPHYTE 
those relatively few cases among Bryophytes where the radial symmetry is 
departed from. 
Among the Liverworts the only recorded example of departure from 
the radial symmetry is that of JAZonoclea: here the sporogonial head. 
which is borne upon a cylindrical seta, is curved over to one side, and 
it dehisces along the upper surface by a longitudinal slit, the whole 
capsule widening out later into a spoon-like form. Examination of 
developmental stages shows that 
the young sporogonial head is 
cylindrical in structure. The 
accepted version of this is that 
the capsule is developmentally 
four-valved, but that dehiscence 
is by one slit only, and accord- 
ingly that the four valves remain 
coherent ; but transverse sections 
of the mature capsule show no 
evidence of a structural dorsi- 
ventrality: the transverse section 
is radial up to maturity, and 
there is no apparent structural 
provision for dehiscence. The 
natural conclusion will be that 
Monoclea shows only a. slight, 
and ontogenetically late and 
unimportant deviation from the 
Splachnnm luteum. 1. Capsule open. 4=apophysis. usual radial type. There are no 
II. Unopened capsule in longitudinal section. s=seta; i if ; 
Lx=leptoxylem; sf=stomata on apophysis; c/=colu- observations connecting this with 
mella ; /=peristome ; -4s=archesporium 3 7=intercellular 
space. II]. and 1V. Diagrams to illustrate the opening external causes. 
of the capsule. (From Goebel, after Hedwig, Vaizey, and 
sryhn.) The sporogonia of most 
Mosses are also of the radial 
type throughout; but in a considerable number a more or less marked 
dorsiventrality is seen in the mature condition. The radial construction is 
as a rule accurately maintained in those sporogonia which grow vertically 
upwards, such as Sphagnum Phascum, or Orthotrichum, and all sides appear 
equally developed in the longitudinal section (Fig. 103. 3). But in many 
an unequal development is found, which is in relation to the position 
which they assume. As maturity is approached they curve to one side, 
and the capsule becomes oblique, or may even hang over. In_ these 
cases the earlier stages of the sporogonium are radially constructed, but 
an inequality appears on the two sides, with, it may be, a_ slightly 
greater development of the assimilating tissue on one side than on the 
other, as in Aunaria (Fig. 103.5): or this may be carried to such an 
extent that the sporogonium is markedly lopsided, as it is found to be 
in the Buxbaumieae (Fig. 103. 8, 9, 10). 
