THE ACHROMATIC FIGURE, CYTOKINESIS, AND CELL WALL 181 



the influence of the centrosome. Biitschli (1876), who looked upon 

 protoplasm as alveolar in nature, held that the rays are not really fibers, 

 but only the lamellae between radially elongated alveolae about the cen- 

 trosome. It was the opinion of Wilson (1899) on the other hand, that 

 the rays are actual fibers, though their material is derived from the 

 alveolar walls. Klein (1878) and others who believed protoplasm to be 

 ultimately fibrillar or reticular in structure, regarded the rays as radially 

 arranged fibrillse. Van Beneden (1883) supposed these fibrillae to be 

 derived partly from the intranuclear reticulum, and Rabl (1889) 

 pointed out that they are continuous with the unaltered cytoplasmic 

 meshwork and arise by a direct transformation of the latter. In Passi- 

 flora Williams (1899) found that the nuclear membrane forms a meshwork 

 connecting the linin reticulum with the cytoplasmic reticulum, all three 

 together organizing the spindle. 



Special Substance Theories. According to another group of theories 

 the spindle and asters are not formed merely by the rearrangement of a 

 structure already present, but arise from a special substance in the cell. 

 This substance was held by some to be a constantly present constituent 

 of the cell, forming the achromatic figure at the time of mitosis and re- 

 maining in reserve through the resting stages. Boveri's archoplasm 

 hypothesis in its earlier form (1888) was a prominent development of 

 this idea. According to this hypothesis the attraction sphere is composed 

 of a distinct substance called archoplasm, which consists in turn of fine 

 granules or microsomes aggregated about the centrosome as a result of 

 the centrosome's attractive force. The entire achromatic figure was 

 held to arise from this mass of archoplasm, the fibers and astral rays 

 growing out from it like roots, to be withdrawn again into the daughter 

 masses of archoplasm at the two poles during the closing phases of mitosis. 

 In this way each daughter cell was thought to receive half of the archo- 

 plasm. Although other workers (Watase 1894) also held that the fibers 

 are outgrowths of the centrosome or centrosphere substance, it was made 

 evident later that the material composing the fiber comes from the cyto- 

 plasm, being added to the growing fiber at its end. This was the view of 

 Driiner (1894, 1895). Boveri later (1895) modified his archoplasm hypo- 

 thesis, adopting the view that the fiber is formed from the substance of 

 the cytoplasm and not necessarily from a constantly present archoplasm. 



Another theory based on the idea of a special substance in the cell 

 was that of Strasburger (1892, 1897, 1898). Strasburger held that the 

 cell has two kinds of protoplasm: an active fibrillar kinoplasm and a less 

 active alveolar trophoplasm. The former constitutes the ectoplast, centro- 

 somes, the mitotic fibers, and the contractile substance of cilia and 

 allied structures. The kinoplasm is thus concerned with the motor 

 work of the cell, whereas the trophoplasm has to do chiefly with 

 nutrition. 



