GRASSES. 



[ 298 ] 



GRIFFITHSIA. 



British species very variable in their appear- 

 ance ; mostly whitish or yellow, papery ex- 

 pansions on bark, beset with irregular black 

 markins;s like writino:. 



BiBL. Leighton, Ann. N. H. 2 ser. iii. 264. 



GRASSES.— A family of Monocotyledo- 

 nous Flowering Plants remarkable in many 

 respects for their microscopic structmes, 

 especially the sihceous Epidermis and the 

 Starch grains in the EndosperiM, for 

 which see those heads. 



GRATELOUPIA, Ag.— A genus of Cry- 

 ptouemiaceae (Florideous Algae), represented 

 by a very rare British species, G. filicina, 

 rarely growing more than 2 inches high 

 with us. Fructification minute, immersed, 

 favellidia opening by a pore, and cruciate 

 tetraspores vertically placed among the fila- 

 ments of the periphery. 



BiBL. Harv. Brit. Mar. Alg. p. 137. 

 pi. 17 A; Grev. Alg. Brit. pi. 16. 



GREGARINA, Dufour. — The cm-ious 

 organisms of which this genus consists, are 

 placed provisionally among the Entozoaj 

 they have as yet been insufficiently examined, 

 and authors are not agreed as to then* struc- 

 tm'e and nature. 



They exist as parasites within the bodies 

 of animals, and inhabit the intestinal canal, 

 or the cavity of the abdomen. Most fre- 

 quently they are met with in insects, espe- 

 cially their larvae; but sometimes also in 

 Annelida, both aquatic and marine {Lumbri- 

 cus, &c.), in the Crustacea and MoUusca. 



They are microscopic and colourless ; 

 mostly round, oval, fusiform or cylindrical 

 (PI. 16. figs. 25, 2H, 34) J and consist of a 

 smooth transparent cell-wall, enclosing a 

 granular, more or less hquid mass, with one 

 or more nuclei and nucleoli. Sometimes 

 they exhibit a constriction in the middle, or 

 are divided by a transverse septum. In 

 some a process resembling a head is situated 

 at one end ; this may be short, round and 

 obtuse or pointed, or more elongated and 

 fm-nished with reflexed hook-like processes. 

 The Gregarince are capable of motion, which 

 is either that of slow progression, ensuing 

 without contraction of the body, or produced 

 by irregular contraction of the membrane or 

 substance of the body. 



Vibratile cilia have been detected both 

 upon the outer and the inner surface of the 

 membrane, and the internal granules often 

 exhibit molecular motion, especiall}^ after 

 the addition of water. One or more long 

 motionless filaments sometimes arise from 

 the outer surface. 



The membrane and its contents, except 

 the nucleus, are soluble in acetic acid. 



Their method of propagation, if such it be, 

 represents a form of conjugation, and takes 

 place as follows. Two individuals coming 

 into contact by corresponding portions of 

 the body (PI. 16. fig. 34), become shortened 

 and firmly united. A transparent capsule 

 is next formed aroimd the two individuals, 

 Avhich encloses them in a cyst (figs. 26, 30), 

 the adjacent portions of the cell-membranes 

 are absorbed, and the substance of the two 

 bodies becomes intimately fused. Globules 

 or cells are then formed in the contents of the 

 cell, which subsequently assume the form of 

 Navicul(E, and have been called pseudo- 

 naviculae (erroneously navicellcB) (figs. 31, 

 32, 33) ; these are supposed to represent 

 the germs of new Gregarince, which become 

 liberated by the bursting of the cell ; their 

 further development has not been traced. 



It has been supposed that the pseudo- 

 naviculse might really represent Naviculce, 

 and that the cysts containing them were 

 sporangia ; but this view does not appear 

 probable, neither do the pseudo-naviculae 

 possess a coat of silex. 



In some cases it appears that the contents 

 of the two cells in conjugation remain di- 

 stinct until the pseudo-naviculae are formed ; 

 but it is not certain whether each single cell 

 in these instances has not arisen from the 

 fusion of two others. 



A vei-y large number, more than eighty 

 species, of Gregarina have been described 

 and arranged in numerous genera, &c., as 

 is so usual where little more than the form 

 of the organisms is known. 



BiBL. Dufour, Ann. d. Sc. nat. 1837. vii.; 

 Stein, Mailer's Archiv, 1848, Ann. Nat. 

 Hist. 1850. v., and Infus.; Frantzius, Obser- 

 vationes de Gregarinis, 1846; Henle, Mdl- 

 ler's Archiv, 1835. 1845 ; Siebold, Beitr. z. 

 Naturg. d. wirbellos. Thiere, 1839 ; Kolliker, 

 Siebold c^ Kolliker's Zeitschr., 1848 & 1849. 



GRIFFITHSIA, Ag.— A genus of Cera- 

 miaceae (Florideous Algae), with feathery 

 fronds 3 to 6" long, composed of delicate 

 dichotomously-branched filaments consisting 

 of a single row of cells, the branchlets often 

 whorled ; colour crimson or rosy red. The 

 fructification consists of spores, antheridia 

 and tetraspores, all produced in similar situ- 

 ations, namely, at the articulations, where 

 they are surrounded by a kind of involucre 

 formed of short ramelli, to which the tetra- 

 spores and antheridia are attached. The 

 antheridia consist of a kind of shrubbv tuft 



