266 ALGjE. 



and conjugation is effected though the curved tube thus formed by the 

 coalescence of the protoplasts of the two cells. The zygosperm is never 

 formed, as in the Mesocarpaceae, in the connecting tube, but in one of 

 the two cells. Lateral conjugation frequently takes place with groups 

 of four cells, the zygosperms being formed in the two central ones. 



The protoplast formed by either mode of conjugation finally secretes 

 a cell-wall of cellulose, and becomes a zygosperm. Germination some- 

 times takes place while still within the mother-cell ; but most commonly 

 both filaments perish after conjugation, with the exception of the 

 numerous zygosperms, which fall to the bottom, the green endochrome 

 having in the meantime turned to a brick-red colour. It then remains 

 dormant through the winter as a resting-cell or hypnosperm, germinating 

 in the spring. Whether the axis of growth of the new individual is 

 parallel or at right angles to that of the old individual is differently 

 stated by different observers. On the commencement of germination, 

 one end of the zygosperm of Spirog}Ta attaches itself like a root to a 

 stone or to some other alga, so that in the earliest stage of the new 

 individual there is a differentiation between base and apex ; but this 

 soon disappears. The innermost of the three layers of which the cell- 

 wall of the hypnosperm is composed bursts through the other two, and 

 protrudes like a bag. The chlorophyll then arranges itself in spiral 

 bands, with starch-grains within them, and the cell divides by transverse 

 septa into a filament, all the cells being from this time precisely alike. 

 Instances are recorded of filaments persisting through the winter. 

 Hofmeister states that the growth of Spirogyra is intermittent, and that 

 the filaments exhibit a nutation, due probably to differences in the 

 rapidity of growth of different sides of the same cell. Where branching 

 takes place, it appears to be confined to the barren portion of a filament 

 in which z}'gosperms have been formed. 



Although the view is contested by some writers, the process of 

 conjugation is regarded by most as a sexual process, but one of the 

 most rudimentary character, the differentiation of the two conjugating 

 elements being exceedingly slight. As de Bary has pointed out — and 

 his statement is confirmed by nearly all more recent observers — the 

 direction of conjugation is clearly governed by some physiological law, 

 the movement of the protoplasm between the two filaments almost 

 invariably taking place in one direction only, so that one of the two 

 conjugating filaments is entirely emptied, while the other is filled with 

 zygosperms.^ Designating the former as the male and the latter as 

 the female filament, it is frequently the case that the cells of the 



> Hassall, however, asserts and figures the contrary {^British Fresh-water Alg(£y 

 i., p. 130). 



