PALMELLA. 



[ 487 ] 



PALMELLACEiE. 



corresponding lines (fig. 560). Thuret states 

 that he has never found antheridia hitherto, 

 and he beheves that Agardh mistook the 

 hairs or paranemata for them. 



BiBL. Harvey, Brit. Mar. Alg. p. 3/. 

 pi. 6 C, Phyc. Brit. pi. 91 ; Greville, Alg. 

 Brit. pi. 10; Agardh, Sp. Alg. i. p. 112; 

 Nageli, Neuer. Algensyst. p. 180. pi. 5 ; 

 Thuret, Ann. des Sc. nat. 4 ser. iii. p. 12; 

 Kiitz. Phyc. generalis, pi. 22; Al. Braun, 

 Rejuv€7iescence, Sfc. {Ray Soc. Vol. 1853), 

 p. 79. 



PALMELLA, Lyngbye.— A genus of Pal- 

 mellaceae (Confervoid Algae), of which the 

 best-known example is the common P. cru- 

 enta (PI. 3. fig, 3 a). This plant, very com- 

 mon on damp walls in shaded places, appears 

 at first in the form of rosy gelatinous patches; 

 these spread and become confluent until the 

 mass extends sometimes over a great extent 

 of sm'face, as a tough, gelatinous, irregular 

 mass, of the colour and general appearance 

 of coagulated venous blood; when dried up in 

 this state, it forms a horny, somewhat crumb- 

 ling stratum ; if placed in water, portions 

 float to the top in pellucid rosy masses of 

 jelly. In its natural habitats its colour 

 and general appearance become disguised 

 when old by the admixture of OscillatoriecB, 

 and other Confervoid growths. 



When placed under the microscope, the 

 frond appears to be composed of a colourless 

 homogeneous jelly, in which are imbedded 

 globular cells, single or in pairs (from divi- 

 sion), of a beautiful rose-colour (fig. 3 a,b); 

 by the application of reagents, these may 

 be shown to possess a proper membranous 

 coat (c). The contents of the cells appear 

 uniformly granular {b, c), and it would ap- 

 pear that, besides increasing by division, 

 the cells also burst and discharge their con- 

 tents, since patches of minute granules occur 

 imbedded in the jelly (lower figs, of b), pro- 

 bably destined to grow up into the ordinary 

 cells. No zoospores, nor the remarkable 

 phaenomena generally that occur in Proto- 

 coccus, have yet been observed in this, which 

 appears to be a ver}^ distinct genus. The 

 jelly of full-grown fronds (which appears to 

 be derived from the gelatinous softening of 

 the coats of the parent-cells of the successive 

 generations of cells) is often over-grown and 

 traversed by minute filamentous structures, 

 which at first sight seem to belong to it ; but 

 on the application of a high power are found 

 to consist of a very minute Nostochaceous 

 plant, apparently the Anabaina subtilissima 

 of Kiitzing, or Vibrio Bacillus, Ehr. (PI. 3. 



fig. 21), which we find to occur commonly 

 among the Palmellaceous Algae. 



P. cruenta has received an extraordinary 

 number of generic names : Tremella, Byssus, 

 Thelephora, Sarcoderma, Phytoconis, Por- 

 phyridium, Globulina, Coccochloris, and 

 Chaos {\). 



From the examination of specimens of the 

 true " red snow," brought home by Captain 

 Parry (for which we are indebted to Mr. 

 Brown), we incline to regard this as a Pal- 

 mella, distinct generically from the Proto- 

 coccus or Hcematococcus pluvialis of the 

 German writers, with which it is commonlj'- 

 associated. Our specimens consist of a tough, 

 colourless gelatinous substance, containing 

 globular cells difl'ering only in size (PI. 3. fig. 



3 d) from those of Palmella cruenta ; and in 

 the jelly occur also abundance of the minute 

 granules or cellules, which are the discharged 

 contents of the larger cells. The red cells 

 of the red-snow plant tiu*n green when ex- 

 posed to light, if kept moist. More par- 

 ticulars are given on this subject under Red 

 SNOW and Rubefaction of water, and 

 Protococcus. 



Other species of Palmella are described, 

 but most of them are too imperfectly known 

 to allow of definite characters bein» given : 

 P. rosea is perhaps a good species. The 

 forms with a definite frond formerly placed 

 here, P. jjrotuberans, botryoides, &c., will 

 be found under Coccochloris. 



BiBL. Eng. Botany (as Tremella cruenta), 

 pi. 1800; Greville, Sc. Crypt. Alg. pi. 205; 

 Meneghini, Monogr. Nostoc. (Trans. Turin 

 Acad. ser. 2. v.), pi. 6 ; Hassall, Brit. Fr. 

 Alg. pi. 80; Nageli, Einzell. Alg. p. &Q. pi. 



4 D (as Porphyridium), p. 71. pi- 4 H; 

 Kiitz. Sp. Alg. p. 211. See also under Red 



SNOW. 



PALMELLACE.E.— A family of Confer- 

 void Algae, consisting of gelatinous or pul- 

 verulent crusts, growing on damp surfaces, 

 in fresh water or in the sea ; composed of 

 globular or elhptical cells, either more or 

 less adherent together into a definite or in- 

 definite pseudo-membrane orfrond, or loosely 

 aggregated within a definitely or indefinitely 

 formed gelatinous matrix, or loosely coherent 

 in the form of a pulverulent crust. Some 

 authors have imagined that the cells of Coc- 

 cochloris or Palmella are attached to fila- 

 ments included in the gelatinous frond : this 

 is an error (see Palmella). Yellowish or 

 bluish-green, or red, often varying from green 

 to red, and vice versa, during the course of 

 development. Increased by cell-division 



