io- 



vary in size according to the species (compare the stipes-cortex of Penicillus, figs. 163, 168, 

 175). They are very minute in U. flabellum, and so large in U. argentea var. spumosa as to 

 be visible under a pocket lens. These "pores" are the uncalcified apices of the simple or 

 branched lateral appendages of the frond filaments ; and these apices, being flush with the 

 surface, form innumerable "windows" for the entrance of liijht. And these "windows", like the 

 pores of Penicillus, U. conglutinata, &c, presumably escape calcification owing to the bubbles 

 of oxygen which, evolved by the chromatophores lodged inside, cling to the outside of the 

 "windows" (see p. 5). 



Internal structure. The thallus of Udotca is composed of continuous non-septate 

 filaments which, branching dichotomously and repeatedly, more or less in one plane, form a 

 flabellate frond which may be monostromatic as in U. javensis, U. glaucescens, etc, or pluri- 

 seriate as in U. conglutinata, U. flabellum etc. The diameter of the filaments varies with the 

 species from about 25 ( a to 1 00 j;., and is a diagnostic character of some importance. 



According to the structure of the filaments the genus may be divided into two groups v ). 

 In one the filaments are destitute of lateral appendages ; in the other they bear lateral appen- 

 dages which vary according to the species. In the first group the simplest structure is found 

 in U. javensis (fig. 36) which has a persistently monosiphonous stipes, and a monostromatic 

 frond. In l \ glaucescens (figs. 3, 5) the frond remains monostromatic, but the stipes in mature 

 plants becomes branched and corticated, and the base of the frond covered with fibulae. In 

 U. conglutinata (fig. 44) and U.orientalis (figs. 1, 4) the frond is pluriseriate. U. cyathiformis 

 (fig. 2) belongs to the same structural group, but has an infundibuliform frond, not a flabellum. 



In the second group, which is characterised by its lateral appendages, the simplest form 

 is U. papillosa (figs. 17, 37), with monostromatic frond composed of filaments studded on 

 frond and back with papillae (fig. 20), and with a stipes monosiphonous in young stages. The 

 other species all have a compound stipes. In U. vcrticillosa (fig. 1 6) the frond is mono- 

 stromatic above, pluriseriate below ; the upper filaments are closely beset on front and back 

 with 2 — 4-furcate spinose appendages in pseudo-verticils (fig. 23 a). In U. argentea (figs. 57 

 and 15) the frond is distromatic above, pluriseriate below ; and the filaments bear capitate lateral 

 appendages arranged distichously (figs. 58^7, b, c). In l\ flabellum (fig. 26) the filaments are 

 pluriseriate, and the lateral branchlets are fewer in proportion and bear cymoid heads (fig. 2777). 

 In three species forming a section of the second group, the lateral appendages are produced 

 only where they are functionally required, that is, on the exterior surface of those filaments 

 of the pluriseriate frond which are situated superficially on the frond, and the lateral appen- 

 dages are, as explained elsewhere, needed as "windows" (p. 5). These three species are U. 

 indica (fig. 52) with short truncate appendages (figs. 13, 53), U. palmetta (figs. 10, ii) and 

 U. spiuulosa (figs. 55, 56 and 12) with acute, simple, or forked appendages. The same arrange- 

 ment is also found in the lower (pluriseriate) part of the frond of U.verticillosa and U. Wilsoni. 



Cortex. The cortical covering of the frond, as may be gathered from what has been 



1) For the decalcification of specimens the best medium is Perenyi's fluid (4 parts nilric acid 10 7„; 3 parts alcohol: 3 pavts 

 chromic acido.5°/ ). After treatment with this Huid the structure becomes clearly visible. 



