Observations on Spirogyra. 421 



Some Observations on Spirogyra. By Mr Gustav Mann. 

 (With Figs. 1-8, Plate II.) 



(Read lOtli April 1890.) 



The fresh water alga Spirogyra, known to most people as 

 it presents itself as smaller or larger patches floating on the 

 surface of ponds and of slowly flowing waters, seems, how- 

 ever, when in this condition not to be growing normally. 

 About two years ago, while I was Ashing from a boat in 

 Duddingston Loch, near Edinburgh, I accidentally came 

 across large banks of this alga growing at a depth of from 

 four to five feet ; the species found were chiefly *S'. nitida 

 and S. jiigalis, in about equal pioportion ; the individual 

 threads were from 2:^ to 3 feet long, not at all entangled, 

 and in perfectly healthy condition. Tlie bottom of the loch 

 at places where this alga was growing was covered with a 

 brownish-red material, which, on microscopic examination, 

 proved to consist of dead Sjnrogy-ra-ceWs in which the 

 chloroplasts had undergone a peculiar disintegration, giving 

 rise to the formation of pink or reddish granules. 



Each Spi7'ogyra-thread is conveniently divided into an 

 apical, a shaft, and a foot portion. I make this division 

 because there are differences in the cells of these three regions. 



The apical cell is slightly bulged out at its free end, the 

 chlorophyll bands broaden out at the ends nearest the apex, 

 and the cell as a whole seems to be the most vigorous in 

 growth, as I conclude from the fact that I have seen twice 

 division occurring in it, while, in one of these cases, the 

 second cell only, and in the other case not a single cell of 

 the thread — and I examined a piece at least 3 inches long — 

 in either case, showed any indication of division. 



The cells of the shaft are those usually described, and they 

 normally divide. As we approach the lower end of a thread 

 however, the cells appear to divide less regularly ; i.e., some 

 may be far advanced in division, while neighbouring cells 

 show no sign of it. The cells in the lower region of the 

 shaft are slightly longer than those in the upper, but the 

 difference is not so marked in cells formed during the 



