292 Evans .— Vegetative Reproduction in Metzgeria. 
Metzgeria linearis , (Swartz) Aust. 
The original material of this peculiar species was collected by Swartz on 
the island of Santo Domingo. It has since been found in Cuba by Wright and 
in Jamaica by E. G. Britton. The account of the gemmae is largely based 
on Wright’s specimens, which have also served for the figures. M. linearis 
is distinguished from the other known species of the genus by the fact that 
the marginal cells are much elongated and have strongly thickened walls, 
thus forming a distinct border 
If | 1 to the thallus (Fig. 15, a). 
)'The marginal hairs also have 
thickened walls, except when 
they assume the function of 
rhizoids, and are frequently 
sharp-pointed. The gemmi- 
parous branches tend to be a 
little narrower than usual, and 
to be more or less tinged with 
blue. In other respects they 
are essentially like normal 
branches, and show no marked 
indications of being limited in 
their growth. The gemmae 
arise in no definite order. Each 
one begins as a single pro¬ 
jecting alar cell, which becomes 
at once the mother-cell of the 
gemma, thus agreeing with 
M. disciformis. At the time 
of separation the gemma con- 
,, FlG - l k A l-J inec t ris :r Portion of a norma ' thallu3 . sists of an oval or circular 
snowing the differentiated margin, x 300. b. A gemma 
at time of separation. x8o. c. Base of a gemma, showing plate of Cells (Fig. 1^, B), 
the two stalk-cells in a different plane, x 300. D. A 1 • 1 • 1 nr nMr i v on 
germinating gemma. x8o. WHICH IS plane Or neai ly SO. 
It averages about 0*12 mm., or 
six cells, wide. At the base of the gemma two stalk-cells, usually lying 
in a different plane, may be distinguished (Fig. 15, c), while the opposite 
end, with its single apical cell, is often narrowed to a very blunt point. 
The hairs produced are short, thin-walled, and few. They are sometimes 
truly marginal, but are more likely to be displaced to either surface 
indiscriminately. Under these circumstances they are often situated at 
the inner edge of the marginal cells, and thus appear at some little 
distance from the margin. Occasionally, in fact, some of the internal cells 
give rise to hairs. The gemmae present no evidences of dorsiventrality. 
