CONJUGATION. 



[ 167 ] 



CONJUGATION. 



have become separated, but in some cases, 

 as in D. Borreri, conjugation of the filamen- 

 tous groups has been observed ; perhaps 

 this occurs in Desmidium also. In Closte- 

 rium, Penium, Tetmemorus, Cosmarium, &c., 

 the free cells conjugate in pairs. In almost 

 all these cases the mode of union appears 

 to be different from that which is seen in 

 Zygnemaceae, for the external membrane 

 dehisces more or less comjjletely, so as to 

 separate the parent-cells into two valves, 

 while a delicate internal membrane previ- 

 ously lining this is protruded as a sac, to 

 meet its fellow from the corresponding con- 

 jugating individual ; these sac-like processes 

 coalesce, and thus the contents of the cells 

 are enabled to mix. In Hyalotheca dissiliens 

 and Penium Brebissonii, there is said to be 

 union of the primary or outer cell-coat, as in 

 Zygnema. The resulting spore or gonidium 

 is mostly formed in the connecting piece 

 {Closterimn, Cosmarium, Tetmemorus, Hya- 

 lotheca){F\. 6. figs, 1-3), or in one of the cells 

 (Didymoprium Grevillii, and perhaps in 

 Desmidium). In Closterium lineatum it has 

 been observed that the conjugating cells 

 divide completely by constriction of their 

 delicate internal membrane, just before con- 

 jugation, so that the dehiscent primary 

 membranes emit from each parent individual 

 a pan of little sacs in close ai)position, and 

 these meeting their fellows, a double or twin 

 conjugation takes place, and a pair of spores 

 or gonidia is formed. A gelatinous invest- 

 ment is secreted around the conjugating sac- 

 like processes, and the spore is generally at 

 first imbedded in an abundant gelatinous 

 coat. (See Desmidiace.^.) 



In the Diatomaceae there does not appear 

 to be anj'^ delicate internal membrane, like 

 that of the Desmidiacere, concerned in the 

 conjugation. The two conjugating indi- 

 viduals, lying near together, become con- 

 nected together by the excretion of a collec- 

 tion of gelatinous substance, the siliceous 

 coats then dehisce, and the contents of the 

 parent-cells, escaping from the valves, meet 

 between them to unite into a globular mass, 

 which does not become a spore, but gradually 

 acquires the form of the parent. There is 

 no connecting tube here ; only the investing 

 gelatinous matter. In Himantidium and 

 Surirella, one new individual is formed in 

 the conjugation (PL 6. fig. 4) ; in Eunotia, 

 Cocconema, Gomphonema and Schizonema, 

 the contents of the parent-cells appear to 

 divide transversely before extrusion, and 

 thus form a pair of new individuals in the 



conjugation (PI. 6. fig. 5) (as in the case of 

 the spores of Closterium lineatum). A pecu- 

 liar condition occurs in other genera, Cyclo- 

 tella, Melosira, &c., which is supposed to 

 be a conjugation of the divided contents of 

 one frustule. (See Diatomace^.) 



Among the Palmellacese, conjugation has 

 been observed in Coccochloris Brebissonii 

 {PalmoglcBa macrococca, A. Braun), where a 

 pan' of vegetative cells become completely 

 fused, membrane and contents, to form a, 

 spore which acquires a firm coat and oily 

 contents, and passes through a stage of rest 

 before recommencing vegetative develop- 

 ment (PI. 3. fig. 6 c, d). 



Conjugation is stated by some authors 

 to take place also in Vaucheria. Nageli, 

 and still more distinctly Karsten state that 

 the hook-like branchlets conjugate with the 

 inflated lateral branches in which spores are 

 produced (distinct from the gonidia in the 

 ends of the filaments). This point is not yet 

 quite settled (see Vaucheria). Phseno- 

 meua bearing some analogy to this are 

 described also by Al. Braun in Achlya and 

 in Coleoch^te. The supposed conjuga- 

 tion of adjacent cells of a filament in (Edo- 

 yonium and Bulbochcete appears to have no 

 reality. 



The only known case of conjugation in 

 the Fungi, that described by Ehrenberg in 

 Sizygites, a genus of Mildew Fungi, is 

 described under that head. 



The conjugation observed in the animal 

 kingdom, consists in the direct union, by a 

 more or less extensive fusion of the substance 

 of two distinct individuals. InDiplozoon para- 

 doxum the two individuals become united by 

 a cross branch, and the remarkable result is 

 that sexual organs become developed on both 

 bodies after this. Conjugation takes place 

 also in Actinophrys, Acineta, Grega- 

 RiNA and PoDOPHRYA. The results have 

 not been observed (see under the heads of 

 these genera). 



BiBL. Vegetables. Vaucher, Hist, des 

 Conferves; Meyen, Pfianzen-physiologie, iii. 

 413; Hassall, Brit. Freshw. Algce; Kiitzing, 

 Phyc. generalis ; Ralfs, Brit. Desmidieee ; 

 Morren, j^nn. des Sc. nat. 2 ser. v. 257 ; 

 Smith, Ann. Nat. Hist. 2 ser. v. 1.; Thwaites, 

 Ann. Nat. Hist. xx. and ser. 2. i. and iii. ; 

 Al. Braun, Rejuvenescence in Nature, Ray 

 Society's Volume, 1853, p. 283 et seq.; 

 Focke, Physiolog. Studien. Heft ii. 1854 ; 

 Nageli, Algen-systeme, p. 175 ; Karsten, 

 Botan. Zeitung, x. p. 89 (1852); Ehrenberg, 

 Verhandl. Naturf. Freund. i. 98 (1829). 



