16 REPORT 1879. 



The labours of Sfcrasburger, of Auerbach, of Oscar Hertwig, of Eduard 

 van Beneden, Butschli, Fol, and others, here come prominently before us, 

 but neither the time at my disposal nor the purport of this address will 

 allow me to do more than call your attention to some of the more strik- 

 ing results of their investigations. 



By far the most frequent mode of multiplication among cells shows 

 itself in a spontaneous division of the protoplasm into two separate por- 

 tions which then become independent of one another, so that instead of 

 the single parent cell two new ones have made their appearance. In this 

 process the nucleus usually takes an important part. Strasburger has 

 studied it with great care in certain plant-cells, such as the so-called 

 'corpuscula ' or ' secondary embryo-sacs ' of the Coniferse and the cells of 

 Spirogyra ; and has further shown a close correspondence between cell- 

 division in animals and that in plants. 



It may be generally stated as the results of his observations on the 

 corpuscula of the Coniferse, that the nucleus of the cell about to divide 

 assumes a spindle shape, and at the same time presents a peculiar striated 

 differentiation, as if it were composed of parallel filaments reaching from 

 end to end of the spindle. These filaments become thickened in the middle, 

 and there form by the approximation of the thickened portions a transverse 

 plate of protoplasm (the 'nucleus-plate'). This soon splits into two 

 halves which recede from one another towards the poles of the spindle, 

 travelling in this course along the filaments, which remain continuous 

 from end to end. When arrived near the poles they form there two new 

 nuclei, still connected with one another by the intervening portion of the 



spindle. 



In the equator of this intervening portion there is now formed in a 

 similar way a second plate of protoplasm (the ' cell-plate '), which, ex- 

 tending to the walls of the dividing cell, cuts the whole protoplasm into 

 two halves, each half containing one of the newly-formed nuclei. This 

 partition plate is at first single, but it soon splits into two laminae, which 

 become the apposed bounding surfaces of the two protoplasm masses into 

 which the mother cell has been divided. A wall of cellulose is then all at 

 once secreted between them, and the two daughter cells are complete. 



It sometimes happens in the generation of cells that a young brood of 

 • cells arises from the parent cell by what is called 'free cell- formation.' 

 In this only a part of the protoplasm of the mother cell is used up in the 

 production of the offspring. It is seen chiefly in the formation of the spores of 

 the lower plants, in the first foundation of the embryo in the higher, and in 

 the formation of the endosperm— a cellular mass which serves as the first 

 nutriment for the embryo — in the seeds of most Phanerogams. The for- 

 mation of the endosperm has been carefully studied by Strasburger in the 

 embryo-sac of the kidney bean, and may serve as an example of the pro- 

 cess of free cell-formation. The embryo-sac is morphologically a large 

 cell with its protoplasm, nucleus, and cellulose wall, while the endosperm 

 which arises within it is composed of a multitude of minute cells united 



