DRAPARNALDIA. 



[ 216 1 



DUMONTIA. 



distinguished (as limited here in accordance 

 v.'ith Kiitziug) by the filaments being com- 

 ])osed of an axis of cells of much greater 

 diameter than that of the cells forming the 

 branches (fig. 182). The species placed here 



Fig. 182. Fig. 183. 



Draparnaldia glomerata. 

 Fig. 182. Portion of a filament. Magnified 200 diams. 

 Fig. 183. Portion of a branch discharging zoospores 

 from its cells. Magn. 400 diams. 



by Hassall and others, devoid of this charac- 

 ter, will be found under Stigeoclonium. 

 The green contents of the cells form a broad 

 band in the middle of the cell ; the mem- 

 brane of the DraparnaldicB, like that of the 

 Chatophorce, is very fugacious, and the fer- 

 tile cells soon dissolve after discharging the 

 zoos)3ores ; the latter have four ciha (the 

 cilia have been omitted in our cut, fig. 183). 

 The assemblages of filaments are gelatinous. 

 Three British species are described : 



1. D. ^/omera^a, Ag. (fig. 182), Principal 

 filament about 1-800" in diameter, irregularly 

 branched; ramelh 1-2400 to 1-3000", in 

 ovate tufts, generally alternate, and patent. 

 Hassall, Br. Fr. Alg. pi. 13. 1 ; Engl. Bof. 

 p. 1746; Vauch. Conferves, pi. 12. fig. 1. 

 Common in streams and wells. 



2. D. j)lumosa, Ag. Principal filaments 

 somewhat pinnately branched, size about the 

 same as the preceding; ramelh in linear- 

 lanceolate tufts, mostly approximated to the 

 axis. Vauch. pi. 11. fig. 2 (Kiitzing refers 

 Hassall's plumosa {I. c. pi. 12. fig. 1) to D. 

 opposita, Ag. as doubtful). Common in 

 streams and wells. 



3. D. repetita, Hass. Principal filaments 

 composed of repeated series of cells, each 

 series consisting of five or six cells, diminish- 



ing in size from the lowest to the highest, 

 the series adjoining each other obliquely; 

 tufts of ramelli dense, alternate. Hass. /. c. 

 pi. 12. fig. 2. Rare. 



See Stigeoclonium. 



BiBL. Bory, Annales du Museum, xii. ; 

 Vaucher (as Batrachospermum), Conferves 

 d'Eau douce ; Link (as Charospermum), Hot. 

 jjJiys.m.; Hassall, I. c. p. 118; Decaisne, 

 Ann. des Sc. nat. 2 ser. xvii. p. 314 ; Thuret, 

 ihid. 3 ser. xiv. p. 15. 



DREPANOPHYLLEiE. — A family of 

 operculate Acrocarpous (terminal-fruited) 

 Mosses; containing only one East Indian 

 genus, Drepanophyllum, Rich., imperfectly 

 known in its details. 



DRIMYS, Forst.— A genus of Magno- 

 liaccce (Dicotyledonous Plants), remarkable 

 for the microscopic structure of the wood. 



See WlNTEREiE. 



DRYOSTACHIUM, J. Sm.— A genus of 

 Polypodiese (Ferns) with very much branched 

 anastomosing veins, with free branches in the 

 meshes. 



DUCK-WEED. See Lemna. 



DUCTS. — A term used in structural bo- 

 tany, applied to those forms 

 of the so-called vascular tissue 

 which consist of long tubes 

 constructed out of perpendi- 

 cular rows of cells, which are 

 thrown into one by the ab- 

 sorption of their adjoining 

 ends. Ducts are thus easily 

 distinsruished from vessels 

 (which taper ofi^ to closed ends) 

 by the constrictions upon the 

 walls of the tubes, indicating 

 the junctions of the compo- 

 nent cells (fig. 184). See 

 Tissues, vegetable, and 

 Vessels. 



DUDRESNAIA, Bonnem.— A genus of 

 Cryptonemiaceae (Florideous Algae), contain- 

 ing two minute British species, with delicate, 

 branched, fihform fronds, a few inches high, 

 of rose-red or reddish-brown colom*. Both 

 D. coccinea, which is a very rare plant, and 

 seldom found except on the south coasts of 

 England and Ireland, andD. Hudsoni, a not 

 uncommon sea-weed, present very elegant 

 microscopic structure, the fronds being com- 

 posed of a central cellular axis, clothed with 

 tufts of delicate, dichotomous, moniliform 

 filaments, standing perpendicularly upon it. 



BiBL. Harvev, Brit. Alg. p. 154. pi. 21 C. 

 Phyc. BnY.pl. 110. 244. 



DUMONTIA, Lamx.— A genus of Cryp- 



Dotted duct from 

 the Melon. 



Magn. 250 diams. 



