F. Cavers. 
i 24 
chantin' 1 and Dumortiera , 2 either from the grooves in the stalk or 
from the sterile lobes between the groups of archegonia. 
In Marchantia and Lunularia , asexual reproduction is exten¬ 
sively carried on by means of specialised organs, the gemmae, 
produced in crescent-shaped ( Lunularia ) or cup like ( Marchantia) 
receptacles on the dorsal surface of the thallus. These gemmae 
have been described and figured in various text-books and have formed 
the subject of much interesting physiological work. At the point 
where a receptacle is about to be formed, the development of the 
ordinary air-chambers of the thallus ceases for a time and a shallow 
depression is formed. At the margin of this depression, either only 
on the side farthest from the growing-point of the thallus (Lunularia) 
or all round ( Marchantia ), the air-chamber tissue grows up to form 
a ridge, which is in Marchantia cut up into numerous long triangular 
lobes. Each gemma is formed from a single cell, which grows up 
and first becomes divided by a transverse wall; the upper cell gives 
rise to the gemma, the lower one remains undivided and forms the 
short stalk. The gemma remains throughout bilaterally symmetrical 3 
and when fully formed consists of an oval disc, several cells thick in 
the middle and thinning out towards the margin, which shows two 
lateral notches at opposite points. Between the gemmae there 
grow out long club-shaped hairs; the mucilage secreted by these 
hairs swells up on absorbing water and causes the gemmae to be 
torn from their short stalks, the loosened gemmae then being washed 
away by rain-drops. Most of the cells of the gemma contain 
chlorophyll, and scattered through its tissue there are several cells 
each containing a large oil body. Certain of the superficial cells, 
on both sides of the gemma, are distinguished from their neighbours 
by their large size and dense protoplasmic contents; these cells, 
which are devoid of chlorophyll, project from the surface of the 
gemma. When the gemma is sown, whichever of its two surfaces 
happens to come into contact with the soil, and therefore is farthest 
from the light, becomes and remains the ventral surface of the 
young plant. One of the growing-points, situated in the lateral 
notches of the gemma, becomes the apex of the thallus; sometimes 
both of these growing-points become active. In the dorsal region 
1 Klein, J , Ueber Sprossung an den Iufiorescenzstielen von 
Marchantia polymorpha. Botan. Centralblatt, Band 5, 1*881, 
p. 26. 
2 Lindberg, S. O., Hepaticaein Hibernia niense Julii 1875 lectae. 
Acta Soc. Sci. Fennicae, Vol. 10, 1875, p. 468. 
3 Pfeffer, W.. Studien uber Symmetrie und specifiscbe Waclis- 
thumsursachen. Arb. des botan. lust., Wurzburg, Band 1, 
1874, p. 77. 
