ZYGOSPORES. 2^^ 



base and apex. This occurs in a much higher degree in the Zygomycetes, and 

 even in the Myxomycetes, which, growing on a substratum, send up their gonidio- 

 phores and sporocarps into the air. 



A non-sexual reproduction takes place universally, but in different ways. In 

 the Pandorineae, Desmidiese, and Diatomaceae every cell-division may be regarded 

 as a vegetative multiplication, since every single cell constitutes an individual; but 

 in the Hydrodictyeae and in Ulothrix peculiar zoogonidia are formed, different 

 from the ordinary vegetative cells. Propagation by gonidia takes place however 

 in the most perfect form in the Zygomycetes, where, before the formation of the 

 zygospores, receptacles are produced on long stalks which develope endogonidia 

 in vesicular swellings, the so-called sporangia, or conidia (stylogonidia) on branched 

 stalks. In many Zygomycetes the much-branched cellular filament which forms 

 the mycelium may break up under unfavourable vital conditions into a number of 

 spherical cells or gonidia, each of which may subsequently reproduce the plant. 



Many Zygosporeae recall the Protophyta in this respect, that they have also con- 

 ditions, during their true vegetative period, in which they have the power of motion ; 

 this occurs to an especially high degree in the Pandorineae and Myxomycetes, much 

 less so in some Conjugates and Diatomaceae. 



FORMS CONTAINING CHLOROPHYLL. 



A. Conjugation takes place between motile cells [Zoosporece). 



I. The Pandorine^^ consist of cells which are either isolated or united into 

 coenobia by gelatinous envelopes; the coenobia are either spherical, as in Stephano- 

 \.sph(Bra, ellipsoid, as in Pandorina, or are square plates, as in Gonium. In these states, 

 [although surrounded by a cell- wall, they have still a power of motion, each cell pos- 

 [sessing two long cilia which protrude through the cell-wall. The isolated cells of 

 fChlamydomonas and Chlamydococcus swim about in this manner like ordinary zoogonidia; 

 [in the coenobia, on the contrary, the cilia of all the individual cells project through the 

 [common envelope, and, by their united action, set the whole ccenobium in a twisting 

 [and rolling motion. The course of life of these plants may be illustrated in two 

 [iexamples. 



The genus Chlamydomonas consists of isolated zoogonidia which multiply in the 



regetative state by hi- or quadri-partition. But in the sexual reproduction the zoogonidia 

 [divide into eight motile daughter-cells each, provided with four cilia, differing from 

 [one another in size but smaller than the mother-cells. According to Rostafinski these 



:ells conjugate in precisely the same way as Pringsheim has described in the case of 



'^andorina {'vide infra) ; the zygospores thus formed come to rest and continue to grow 

 for some weeks ; if then dried and again placed in water they divide repeatedly, and 

 Form resting motionless families of cells identical with the genus Pleurococcus formerly 



)laced under Palmellaceae. 



^ Cohn, Ueber Chlamydococcus und Chlamydomonas, Berichte der schles. Ges. 1856. [Ray Soc, 

 Bot. and Physiol. Mem. 1852.] — Cohn und Wichura, Ueber Stephanosphcera pluvialis. Nova Acta 

 Acad, nat. curios, vol. XXVI. p. i. [Quart. Journ. Micr. Sc. 1858, p. 131; Archer, ib., 1865, 

 pp. 1 16-185.] — Pringsheim, Ueber Paarung der Schwarmsporen, Monatsber. der Berliner Akad., Oct. 

 1869. [Ann. des Sc. Nat. 1869, vol. XII.]— De Bary, Bot. Zeitg. 1858, p. 73.— Rostafinski, Bot. Zeit. 

 1871, p. 787. 



