Vegetative Reproduction in Metzgeria. 
BY 
ALEXANDER W. EVANS. 
With sixteen Figures in the Text. 
T HE organs of vegetative reproduction in Metzgeria are so conspicuous 
that they attracted the attention of observers at a very early date. 
They consist of thalloid structures, usually but one cell thick throughout, 
and easily become detached at maturity. Each one arises from a single 
cell of the parent thallus, either from an alar cell or from one of the cortical 
cells of the costa. The position of the reproductive bodies on the thallus 
varies in different species. In some they are always marginal, while in 
others they are borne on the upper, or antical, surface of the wings. In 
still other species, where they are produced on strongly specialized branches, 
their position is much more indefinite, any superficial cell being apparently 
able to assume the reproductive function. It has been customary to 
designate these reproductive bodies as ‘ adventive branches' when they 
arise from marginal cells of the thallus, and as ‘ gemmae ’ or * bulbils ’ 
when they arise elsewhere. It has already been shown, however, by 
Schostakowitsch (’ 94 , p. 350) and others that there is no essential differ¬ 
ence between them, either in their development or in the way in which 
they become detached from the parent plant. In the present paper, there¬ 
fore, they will be spoken of as ‘ gemmae ’, whatever their position. The 
term 1 adventive ’ may then be retained for branches which arise from the 
postical surface of the costa, and in the development of which the internal 
costal cells take part. Strictly speaking, such branches are not reproduc¬ 
tive structures at all, although they may eventually give rise to new indi¬ 
viduals through the progressive dying away of the old thallus. The 
differences between adventive branches of this character and gemmae are 
usually well marked, but they sometimes become less definite on poorly 
developed individuals. 
Apparently, Hooker (T6, pi. 55) was the first one to describe the 
gemmae of Metzgeria clearly. He studied them in what he called Jimger- 
mamiia [now Metzgeria ] furcata y aeruginosa , a plant characterized by a 
peculiar bluish-green colour and by specialized gemmiparous branches. 
The next writer who added substantially to our knowledge was Nees von 
[Annals of Botany, Vol. XXIV. No. XCIV. April, 1910.] 
