DRAPARNALDIA. 



[ 271 ] 



DUDRESNAIA. 



and by resting-spores formed in the same 

 situation and set free by the solution of the 

 walls. 



Fig. 179. 



Fig. 180. 



Draparnaldia glomerata. 



Fig. 179. Portion of a filament. Magnified 200 

 diams. 



Fig. 180. Portion of a branch discharging zoospores 

 from its cells. Magn. 400 diams. 



D. glomerata , Ag. (fig. 179). Principal 

 filament about 1-800" in diameter, irregu- 

 larly branched ; ramelli 1-2400 to 1-3000", 

 in ovate tufts, generally alternate, and pa- 

 tent. Hassall, Alg. pi. 13. 1 j Engl. Hot. 

 1746 ; Vauch. Conferves, pi. 12. fig. 1. Com- 

 mon in streams and wells. 



D. plumosa, Ag. Principal filaments 

 somewhat pinnately branched, size about 

 the same as the preceding ramelli, in linear- 

 lanceolate tufts, mostly approximated to the 

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

 Hassall's plumosa, 1. c. pi. 12. fig. 1, to D. 

 opposita, Ag. as doubtful). Common in 

 streams and wells. 



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. I. c. 

 pi. 12. fig. 2. Rare. 



See STIGEOCLONIUM. 



BIBL. Bory, Ann. Museum, xii. ; Vau- 

 cher (as Batracliospermuni), Conferves d'Eau 

 douce ; Link (as Charospermum),Hor. Phys. 

 iii. j Hassall, Algce, 118 ; Decaisne, Ann. 

 Sc. Nat. 2 ser. xvii. 314 ; Thuret,. 3 ser. 



xiv. 15; Currey, Qu. Mic. Jn. vi. 207, 

 pi. 9; Hicks, ibid. 1869,383; Rabenhorst, 

 Fl. Alg. iii. 381. 



DREPANOS'IPHON, Koch. A genus 

 of Aphidse. 



D. platanoides, and D. acerina, on the 

 sycamore. (Buckton, Aphid., Ray Soc. i. 

 182.) 



DRI'MYS, Forst. A genus of Magno- 

 liacese (Dicotyledonous Plants), remarkable 

 for the microscopic structure of the wood. 

 See WINTERED. 



DRY ROT. A peculiar decay in wood, 

 caused either by the presence of Fungi, as 

 Merulius lacrymans and Thelephorapateana, 

 or by a chemical process known under the 

 name of Eremacausis or gradual combustion. 

 Many remedies have beeen proposed ; sul- 

 phate of copper, corrosive sublimate and 

 creosote, especially the latter, are amongst 

 the most approved. In domestic architec- 

 ture, a free circulation of air and exclusion 

 of moisture are essential. 



DRYMOGLOS'SUM, Presl. A genus 

 of Grammitideae (Polypodiaceous Ferns). 

 D. cornosum, exotic. 



DUCTS. A term applied in structural 

 botany to those forms of ~Fig. 181. 

 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 

 distinguished from vessels, 

 which taper off to closed ends, 

 by the constrictions upon the 

 walls of the tubes, indicating 

 the junctions of the compo- 

 nent cells (tig. 181). See Doto5dductfrom 

 TISSUES, VEGETABLE; and the Melon. 



VESSELS. Magn. 250 diams. 



DUDRESNAI'A, Bonnem. A genus of 

 Cryptonemiaceae (Florideous Algse), con- 

 taining two minute British species, with 

 delicate, branched, filiform fronds, a few 

 inches high, of rose-red or reddish-brown 

 colour. D. coccinea, which is a very rare 

 plant, and seldom found except on the 

 south coasts of England and Ireland, and 

 D. Hudsoni) a not uncommon sea-weed, 

 present very elegant microscopic structure, 

 the fronds being composed of a central 

 cellular axis, clothed with tufts of delicate, 

 dichotomous, moniliform filaments, stand- 

 ing perpendicularly upon it. The fructify- 

 ing process in this genus is very complicated. 



