o 



74 BULLETIN OF THE 



swollen extremities. The whole cask-shaped nucleus undergoes a length- 

 ening meantime, so that the two segments have made only comparatively- 

 little advance toward the ends of the nuclear structure. Both the nu- 

 cleus and the surrounding protoplasm are in great commotion, and the 

 latter is often radially disposed at the ends of the nucleus (p. 44). There 

 appears a granular accumulation in the equatorial plane of the [inter- 

 zonal] filaments, and into this median zone the latter are at length ab- 

 sorbed. About this time the protoplasm, which ensheathed the sides of 

 the nucleus, is differentiated into a few (ca. 15) filaments [not nicclear 

 filaments !], which are attached behind the disks (i. e. on their polar 

 faces) in a circle. 



When the interzonal filaments disappear, the granules of the lateral 

 segments begin to fuse with each other and with the striated nuclear sub- 

 stance (nuclear fibres) which still remains between this structure and 

 the ends of the lengthened cask-shaped nucleus. Thus solid disks are 

 formed. The latter soon move into contact with the granular protoplasm 

 which covers the ends of the cask-shaped structure. Each of the extra- 

 nuclear filaments * soon presents at both its extremities — in the granular 

 protoplasm covering the polar surfaces of the nuclear disks — a little 

 swelling, and at the same time the course of the filaments becomes more 

 convex outwardly. The equatorial granular accumulations of the inter- 

 zonal filaments are ultimately transferred to these extranuclear filaments, 

 and they in turn unite with the ingrowing girdle of mural protoplasm. 

 Meantime the equatorial faces of the homogeneous solid disks become 

 convex ; there soon appears in each disk a few (2-4) highly refractive 

 globular bodies, all but one of which are gradually dissolved and disap- 

 pear ; this one increases in size and becomes the nucleolus ; it eventu- 

 ally comes to occupy the centre of the nucleus (disk), both faces of the 

 latter having meantime become convex. By the distribution of the gran- 

 ular protoplasm over the whole surface of the two new nuclei, the latter 

 are in all essentials like the nucleus from which they were derived. 



With this more detailed account for Spirogyra the other studies of 

 Strasburger on plant cells may be summarized by considering some of 

 their deviations from the case just reviewed. Besides algae the cells 

 of various higher plants were studied, principally by means of alcoholic 

 preparations. Stomatic and endosperm cells, the parent cells of pollen 

 and spores, the hairs of Tradescantia stamens, etc., exhibited essentially 



* By this name I would designate those filaments which are formed from the 

 protoplasm lying outside the cask-shaped nucleus, and which Strasburger calls " Ver- 

 bindungsfaden. " 



