Spirogyrex 351 



containing little or no chlorophyll, whereas the other cell increases in size 

 develops one or more chloroplasts, and by repeated divisions forms a filament. 

 Except in one or two species of Spirogyra the distinction between base and 

 apex is soon lost and the filaments float freely in the water ; thus the slight 

 rhizoidal development which sometimes occurs is of little practical value since 

 the filaments almost immediately become free-floating. In some cases organs 

 of attachment (haptera) are developed subsequently from older cells, and in 

 Spirogyra adnata several of the adjacent basal cells may participate in the 

 formation of attaching organs (Delf, '13). 



It has been disputed that Spirogyra exhibits any sexuality, but there are many facts 

 which suggest a differentiation of sex. The cell containing the zygospore becomes in some 

 species greatly inflated, a distention which is never observed in the emptied cell. That 

 part of the conjugation-tube developed from the cell in which the zygospore is lodged is 

 very often thicker and shorter than the part developed from the opposite cell, and in some 

 cases (e.g. Sp. punctata Cleve, Sp. tenuissima Hassall, Sp. orientale W. & G. S. West) it 

 may not be developed at all or is obliterated by the distention of the cell. The location of 

 the zygospore in that gametangium which shows these special characters indicates that 

 there is a differentiation of sex similar to that which occurs in Zygnema. 



In most cases the cells of one filament become all of the same sex and two filaments 

 only are concerned in scalariform conjugation, but three, four, five, six, or even more may 

 occasionally take part in one conjugating example (consult fig. 218.4). Statistics show 

 that in these cases the female filaments predominate (a condition frequently termed 

 ' polygamy '), the relatively shorter length of many of the cells of a male filament often 

 permitting of the formation of sufficient male gametes to supply two female filaments. 



Lateral conjugation, or conjugation between adjacent cells of the same filament, is 

 much more frequent in Spirogyra than in Zygnema, and is the general rule in certain of 

 the more slender species, such as Sp. tenuissima, Sp. inflata (fig. 218 D), Sp. quadrata and 

 others. It also occurs in large species like Sp. majuscida. In these cases a differentiation 

 of sex must take place amongst the cells of the same filament, some becoming male and 

 others female. In rare instances scalariform conjugation takes place between filaments 

 with this promiscuous differentiation of sex, perfectly normal zygospores being formed in 

 the female cells of each filament. This type of conjugation has been termed ' cross- 

 conjugation' (vide W. & G. S. W., '98, t. v, f. 81). 



Irregularities are frequently met with in conjugating filaments. Zygospores are 

 occasionally observed which have been produced by the fusion of three gametes, two male 

 and one female (W. W., '91 ; Borge, '91 ; W. & G. S. W., '98), but such attempts are usually 

 abortive (fig. 218 E ; consult also W. & G. S. W., '98 ; Schmula, '99 ; etc.). Copeland ('02) 

 states that in these cases the nucleus of the abortive male cell is situated against the wall 

 opposite toandremote from the conjugation-canal. Gerassimoff has observed the conjugation 

 of two female cells with one male cell and the formation of the zygospore by the fusion of 

 the male gamete with one female gamete, a parthenospore being formed by the other female 

 gamete. Owing to sudden changes of the physiological conditions it not infrequently 

 happens that conjugation is brought to an abrupt termination before the fusion of the 

 gametes has taken place. In such cases parthenospores are often formed, either one in 

 each gametangium or two in the female gametangium (vide Rosenvinge, '83 ; W. W., '91 ; 

 Hansgirg, '88; W. & G. S. W., '98; etc.). The discovery by Gerassimoff of binucleated 

 cells in the Zygnemacese may perhaps afford a,n explanation of some of these irregularities 



