A crogynous J lingermanniales. 
281 
Fig. 50. Diagrammatic longitudinal sections of various Acrogynae, 
showing the archegonial group and the sporogonium with the structures 
developed around them. I.—Perianth and involucre free (e.g., Lophocolea, 
Plagiochila, Fnillania). II.—Perianth and involucre “fused”— i.e., carried up 
by the growth of a basal ring-like zone of stem tissue (e.g., Eucalyx). III.— 
Perianth and involucre “fused”; the formation of an incipient marsupium 
(“fruit-sac”) indicated by the bulbous swelling of the stem below the foot of 
the sporogonium (e.g., Narclia geoscypha) IV.—The seta and foot of the 
sporogonium have penetrated for some depth into the stem tissue (e.g., 
Ceplmlozia bicuspidata). V. and VI.-—Two stages in the development of 
“ccelocauly”—the complete embedding of the sporogonium in the stem tissue 
e.g., Gottschea, 1'vichocolea). VII. to IX.—Three stages in the development of 
the erect marsupium of Isotachis. Arch., archegonia; cal., calyptra; caps., 
capsule; emb., embryo sporophyte ; f., foot; inv., involucre ; 1., leaf; mars., 
marsupium ; per., perianth ; se., seta ; st., stem. Figures IV. to IX. are from 
Goebel. 
perianth, involucre—are free from each other and the sporogonium 
foot extends only to about the insertion of the involucre, we may 
trace various lines of specialisation, resulting in the more complete 
investment of the young sporogonium, and culminating in the various 
types of fruit-sac which can be distinguished among the marsupial 
Acrogynae. 
Among the various processes which tend to facilitate the 
nursing of the young sporogonium, and of which several may take 
place hand in hand, the simplest is the following. The seta, capped 
by the absorbing foot or haustorium, grows actively downwards 
into the stem tissue, which may either remain unaltered or may 
grow in thickness so as to form a thick protective and food-storing 
sheath around it. In many cases, the foot penetrates below the 
insertion of the involucre, so that only the capsule and upper part of 
the seta of the ripe, but not yet exserted, sporogonium are covered by 
the calyptra, but no further special development occurs (Fig. 50, IV.). 
In other cases, however, the portion of stem underlying the 
archegonial group grows actively, in such a way that more and 
more of the lower portion of the sporogonium becomes sunken in 
it and surrounded by a thick sheath formed of stem tissue, while 
the calyptra gradually dwindles in size. In Leiomitra, the calyptra 
is still recognisable as a thin envelope covering the capsule itself. 
In the allied genera Trichocolea and Polyotus, there is no calyptra 
at all, if we limit the idea of a calyptra to the result of growth of 
the archegonium venter; the so-called “calyptra” is here in reality 
formed from the stem tissue, into which the lower end of the 
sporogonium burrows deeply, and which bears at the apex the 
unfertilised archegonia (and the neck of the fertilised one), while 
the involucral leaves are either carried up on its sides or form a 
crown at the top (Fig. 50, V., VI.). In the three genera just 
