Observations on Spirogi/ra. 427 



scopical study, is proved by two facts : Firstly, the nuclei 

 are fully formed, with no indication of a nuclear barrel ; and, 

 secondly, a line drawn between the two nuclei would not be 

 at right angles to the plane of the rudimentary cell wall, 

 and would not pass through the centre of this plane, as one 

 of the nuclei is usually found close to the side of the mother 

 cell, or even both nuclei may be on one side of the partition, 

 the other half of the cell having no nucleus. 



I shall conclude this paper by recording some miscel- 

 laneous observations made while studying the chlorophyll- 

 bands, specially with regard to changes in the shape of the 

 chlorophyll-bands, the form of the protein crystals, methods 

 of staining nuclei and threads, &c., and ultimately I shall 

 refer to the occurrence of crystals. The chlorophyll-bands 

 represent on cross section usually a " Y " shape if examined 

 during the day ; but if material which has been kept in 

 the dark for 48 hours is examined, the chlorophyll-bands 

 show an oval or flattened outline (fig. 4). What the cause 

 of this peculiar change is, I cannot state definitely, but one 

 explanation may be this : the pyrenoids are placed in the 

 centre of the chlorophyll-bands and sunk in the substance of 

 the band, and as starch is gradually laid down in them, 

 they will swell, and being pulled towards the nucleus by 

 the threads joining them to it, they will alter the shape of 

 the band, rendering the latter convex on the side next the 

 nucleus, and concave next the cell wall. This view is 

 strengthened by the fact that the more starch is laid down 

 in the pyrenoids, the more marked is the ridge on the sur- 

 face of the chloroplast next the nucleus. This change will 

 also bring about less surface exposure of the band to light, 

 and so diminish the elaboration of starch. 



The threads joining the pyrenoids to the nucleus have 

 a structure as first described by Pringsheim, namely, 

 at the pyrenoidal end they form deeper or shallower 

 cups, enclosing tlie starch-centres or protein crystals, as 

 Strassburger terms them, while at the nuclear end the 

 threads fuse, according to my observations, in two bags, in 

 the shape of hemispheres, the margins of which are united 

 together. The two bags are placed in the long axis of the 

 cell, and are specially well seen in Spirogyra jugalis, if 

 threads be treated first with absolute alchohol and then 



