THE THALLOSE HEPATICAE OF THE JUAN FERNANDEZ ISLANDS 575 



thickened median portion: calyptra and sporophjte not seen: gemmae marginal, 

 borne on undifferentiated and sometimes ecostate thalli, the length variable but 

 often about i cm., the width mostly 0.2 — 0.5 nim., or ten to sixteen cells; costa 

 often absent but sometimes present in a more or less rudimentary form; hairs, 

 if present, few and restricted to the margin. 

 On rocks and ferns. 



Masatierra: Co. Centinela, on BUcJniiim in thickets, 550 m., and on trees, 

 530 m. (no. 50, 51); C. Salsipuedes, on Thyrsoptcris in Z>/cX\\y';//^? forest, 660 m. 

 (no. 52). 



Masafiiera: innermost accessible part of O. de las Casas, on rocks, 200 m. 

 (no. 53, 54); O. del Blindado, on rocks in forest, 440 m. (no. 55); C. del Barril, 

 on dead ferns (no. 56). 



No. 50 may be designated the type. 



As its name implies J/. Diiiltiforniis is an exceedingly variable species, 

 and it owes its variability in great part to its strong tendency to assume re- 

 versionary or juvenile forms. In this respect it resembles the northern M. furcata 

 (L.) Dumort. in certain of its manifestations. Although some of the thalli of 

 J/, multiformis ma\- be costate throughout (Fig. 5, A), others show a well- 

 developed costa only here and there and pass gradually or abruptly into a 

 wholly ecostate condition (Fig. 5, B, C) or into a condition where the costa is 

 only partially differentiated and indistinct. The ecostate thalli are usually narrow 

 but this is by no means necessarily the case. Some of the examples studied, 

 in fact, have been thirty cells across and have thus attained a width of i mm. 

 or more. Thalli of this character occasionally fork but seem to show no indi- 

 cations whatever of dorsiventrality; in other words the ventral surface lacks 

 appendicular organs completely, not even slime-papillae being present. One 

 peculiar manifestation of reversion is shown in Fig. 5, E, which represents a 

 female branch with unfertilized archegonia renewing its growth as a vegetative 

 thallus. 



The marginal gemmae of M. multiformis, which are sometimes produced 

 in considerable abundance, arise in no definite order. The gemmiparous thalli 

 show no evidence of being limited in their growth by the presence of the gemmae 

 and are not morphologically differentiated in an\- wa}-. They may be costate 

 or ecostate (Fig. 5, F. G), and the thalli with costae sometimes produce female 

 branches and gemmae at the same time, showing that neither type of organ 

 inhibits the appearance of the other. The gemmae arise directly from marginal 

 cells which have not undergone a preliminar\' dix'ision. They broaden out 

 gradually from a stalk-like base and apparent!}' never branch before becoming 

 detached; in other respects they are much like ordinar}- vegetative thalli and 

 may be distinctly or indistinctly costate or else entirely ecostate, one condition 

 passing readily into another. As a rule an ecostate thallus gives rise to ecostate 

 gemmae, but exceptions occur; and a costate thallus may bear ecostate and 

 costate gemmae indiscriminately. The gemmae with costae sometimes show a 

 few ventral slime-papillae and a slight displacement of the marginal hairs to 

 the ventral surface, but these are the only evidences of dorsiventrality to be 

 observed. Ecostate gemmae seem to be alike on both surfaces, and the same 



