186 TEAXSACTIONS AND PROCEEDINGS OF THE [Sess. Lxm. 



described as occurring in nature. A few variations are not 

 described in that paper, and of these the following note 

 gives some details. It is interesting to note that all these 

 were found occurring in one culture of Spirogyra. It was 

 impossible to mount the smallest particle of the material 

 without finding in it some abnormality. The particular 

 Spirogyra was not determined, but it was one of the 

 common species of medium size with serrate-edged chrom- 

 atophores and large pyrenoids. 



Gatherings of the material, which had been compressed 

 into small tubes, were turned out into a shallow white 

 glazed dish with just as much water as sufficed to keep the 

 filaments moists The culture was exposed to the diffuse 

 light of a north window, and kept at the ordinary tempera- 

 ture of the laboratory. Tap water was supplied at long 

 intervals as the specimens dried. The specimens were 

 allowed to become dry inadvertently on several occasions. 

 The plants, which were matted and coiled together in inex- 

 tricable confusion, were at first in vegetative condition, but 

 after some weeks all passed into the reproductive stage. 

 Part of the material was examined fresh, the remainder 

 was fixed and preserved in a solution of acetic acid. 



In Spirogyra in nature various modes of conjugation are 

 found, the commonest being the so-called Scalariform. 

 This may be of two types — the normal uniform, where the 

 movement of the protoplasts between the filaments takes 

 place in one direction only, so that one filament is emptied 

 and the other filled with zygospores. The other variety of 

 Scalariform is known as cross conjugation, where the move- 

 ment of the protoplasts between the filaments is not 

 uniformly in one direction, so that ultimately each filament 

 contains a number of empty cells, as well as several cells 

 containing zygospores. This variety is so rare as to be 

 practically abnormal. 



An interruption in conjugation may result in a kind of 

 false cross conjugation, where, although the conjugating 

 tube is formed, there is no movement of the protoplasts, 

 but each rounds itself off into an azygospore. 



A more infrequent mode than normal scalariform, and, 

 possibly, to be regarded as abnormal, is lateral, where con- 

 jugation takes place between adjacent cells of the same 



