HALICHONDRIA. 



[ 315 ] 



HALYMENIA. 



skin of the seed on a slide, in a little alcohol, 

 which does not soften the cell- wall; when 

 the object is focused, the addition of a little 

 water causes the gelatinous softening of the 

 cell-walls, the spnal fibres fly out from the 

 surface of the seed-coat, and show clearly 

 the character of these beautiful objects. 

 The primary membrane may be detected even 

 in its gelatinous state, by adding sulphuric 

 acid and iodine, which produce a purplish 

 or violet colour. Further remarks on this 

 head will be found under Spiral Struc- 

 tures. 



The hairs on the stigma of Campanula 

 are remarkable for the intussusception which 

 is observed to take place in mature hairs. 

 The filiform processes growing from the 

 under surface of the frondose Hepaticacese, 

 the thallus of Lichens, the prothallium of 

 Ferns, &c., are commonly called radicle 

 hairs. In most cases they present no re- 

 markable points of structure ; in Marchantia, 

 however, peculiar spiral markings have been 

 detected (see Marchantia). 



BiBL. General Works on Structural Bo- 

 tany; Meyen, Secretions-organe der PJlan- 

 zen, Berlin, 1837, Pjianzen-pJiysiologie; 

 Cohn, de Cuticula, LinncBa, xxiii. 337, 1850 ; 

 Schleiden, Beitrdge ziir Phytogenesis, Mul- 

 ler's Archiv, 1838, Beifr. z. Botanik, Leip- 

 sic, 1844, i. p. 121 (Transl. in Scientijic Me- 

 moirs) ; Decaisne, Arm. des Sc. nat. 2 ser. 

 xii. 251. pi. 4; Leighton, Ann. Nat. Hist. 

 vi. p. 257 ; Brongniart, Ann. des Sc. nat. 

 2 ser. xii. p. 244. pi. 4. 



HALICHONDRIA, Flem.— A genus of 

 Sponges. 



HALIDRYS, Lyngb. — A genus of Fuca- 

 ceae (Fucoid Algae), containing one British 

 sjiecies, H. siliquosa, common on rocks and 

 stones somewhat above low-water mark. It 

 is readily distinguished by its pod-like, sep- 

 tate air-vessels. The fructification, which is 

 terminal on the branches, much resembles 

 that of Fucus, except that the interior of 

 the receptacles is filled up with firm poly- 

 gonal cellular tissue. The antheridia, more- 

 over, are terminal on their pedicels, often in 

 tufts, short in form, and intermixed with 

 spore-sacs in the same conceptacle. 



BiBL. Harvey,-Br. iV/«r.^/^.p.l5.pl. IC; 

 Thm'et, Recherches sur les Antheridies, Ann. 

 des Sc. nat. 3 ser. xvi. p. 8. pi. 3. 



HALIONYX, Ehr.— A genus of Diato- 

 macese. 



Char. Frustules single ; valves equal, or- 

 bicular, surface radiate, a certain number of 

 the rays not commencing at the umbilicus ; 



no internal septa ; umbilicus not reached by 

 the rays. Marine. 



H. senarius, Rays six, the intervening 

 spaces with shorter rays of equal length pa- 

 rallel to the larger, and with transverse laxly 

 cellular lines ; umbihcus punctate, entire ; 

 diam. 1-720". 



H. duodenarius. Rays twelve. 



Probably forms of Arachnoidiscus. 



BiBL. Ehr. Ber. d. Berl. Akad. 1844. 

 p. 198. 



HALISERIS, Tozzetti.— A genus of Dic- 

 tyotaceae (Fucoid Algae), containing one Bri- 

 tish species, with a bro\^Tiish-olive, some- 

 times forked frond, with a midrib, from 4" to 

 I' high, having a verj^ powerful, offensive 

 smell when fresh. The fructification is pro- 

 duced in sori, arranged in lines on each side 

 of the midrib, or scattered, containing large 

 spores. (This requires further examination.) 



BiBL. Harvey, Br. Mar. Alg. p. 36. 

 pt. 6 B. 



HALTERIA, Duj. — A genus of Infusoria, 

 of the family Keronia. 



Char. Body almost spherical or top- 

 shaped, surrounded by long, very delicate, 

 retracting cilia, which, by becoming adherent 

 to the slide, and suddenly contracting, cause 

 it to change its place suddenly, as if by leap- 

 ing. A row of oblique very large cilia situ- 

 ated at the circumference of the body. 



H. grandinella { = Trichodina grandinella, 

 Ehr.) (PI. 41. figs. 11,12). It has two kinds 

 of appendages on its surface : 1, straight, 

 excessively delicate, radiating cilia, which 

 appear to be the cause of its movements, 

 which are so sudden, that, even wdth the 

 utmost attention, it cannot be ascertained 

 how they are produced ; 2, very large cilia, 

 arranged obliquely at the circumference of 

 the body. Aquatic. Greatest breadth, 

 1-850". 



Stein points out the resemblance of this 

 animalcule to the swarm-germs of an Acineta 

 found upon Cyclops. 



BiBL. Duj ar din, Infus. p. 414; Stein, 

 Infus. p. 54. 



HALYMENIA, Ag.— A genus of Cry- 

 ptonemiaceae (Florideous Algae), containing 

 one British species, found on the southern 

 shores. It is a somewhat palmate, mem- 

 branous, rose-coloured sea-weed, usually 

 from 6 to 12" long, composed of a double 

 membrane, the layers being separated by a 

 loose network of jointed filaments. The 

 fructification consists of favellidia buried in 

 the frond, attached to the inner surface of 

 the membranous laminae ; scattered all over 



