PADINA. 



[ 573 ] 



PALMELLA. 



by a layer of cells much smaller than the 

 rest, forming a kind of epidermis, which 

 ultimately acquires a tluckish cuticular 



Fig. 554. 



Padina i'avonia. 

 Frond, one third natural size. 



layer. The growing edge of the frond is 

 rolled backwards (circinate) and fringed. 

 The fructification occurs in linear concentric 

 sori, on the coloured zones of the frond. 

 The pear-shaped spore-sacs (tig. 555) origi- 

 nate from cells of the epidermal layer, which 



Fig. 555. 



Vertical section of a frond at a concentric ZOIK-, inr.de 

 in a radial direction, cutting through the sorus of spore- 

 sacs and a line of hairs. The indusial layer of cuticle 

 has been removed. 



Magnified 50 diameters. 



take on special development, and in the 

 course of their growth push up and finally 

 burst through the loosened cuticular layer 

 which originally clothed them, so that the 

 latter forms a kind of indusium like that of 

 the Ferns. The spore-sacs produce each 

 four spores, which separate after their escape 

 from the sac. The zones of the sori alter- 

 nate with zones composed of tufts of jointed 

 hairs placed in corresponding lines (fig. 555). 

 Thuret states that he has never found 

 antheridia hitherto, and he believes that 

 Agarclh mistook the hairs or paranemata 

 for them. 



BIBL. Harvey, Mar. Alg. 37, pi. 6 C ; 

 Tliyc. Br. pi. 91; Grev. Alt/. Br. pi. 10; 

 Agardh, Sp. Alg. i. 112; Nageli, Algensyst. 

 IfeO, pi. 5 ; Thuret ; Ann. Sc. Nat. 4 ser. iii. 



12 ; Kiitz. Phyc. gen. pi. 22 ; Al. Braun, 

 Rejuvenescence, Ray Sac., 1853, 79. 



PALMEL'LA, Lyngbye (Red snow and 

 gory dew r ). A genus of Palmellacece (Con- 

 lervoid Algse), of which the best known 

 example is the common P. cruenta (PL 7. 

 tig. 3 a). This plant, very common 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 

 surface, as a tough, gelatinous, irregular 

 mass, of the colour and general appearance 

 of blood ; when dried up in this state, it 

 forms a horny, somewhat crumbling stra- 

 tum ; if placed in water, portions float to 

 the top in pellucid rosy masses of jelly. 



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 (6, c) ; and it would 

 appear that, besides increasing by division, 

 the cells also burst and discharge their con- 

 tents, since patches of minute granules occur 

 imbedded in the jelty (lower figs, of 6), pro- 

 bably de.vtined to grow up into the ordinary 

 cells. No zoospores, nor the remarkable 

 phenomena generally that occur in Proto- 

 coccus, have yet been observed in this, which 

 appears to be a very 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 overgrown and 

 discoloured by minute filamentous struc- 

 tures, 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 Nos- 

 tcchaceous plant, apparently the Anabaina 

 subtilissima of Kiitzing, or Vibrio bacillus, 

 Ehr. (PL 7. fig. 21), which we find to occur 

 commonly among the Palmellaceous AlgaB. 

 From the examination of specimens of 

 the true "red snow," brought home by 

 Captain Parry, we incline to regard this as 

 a Palmella, distinct generically from the 

 Protococcns or Hcematococcus pluvialis of 

 German writers, with which it is commonly 

 associated. Our specimens consist of a 

 tough, colourless, gelatinous substance, con- 

 taining globular cells differing only in size 

 (PI. 7. fig. 3 d) from those of Palmella cru- 

 enta ; and in the jelly occur also abundance 



