80 INTRODUCTION TO CYTOLOGY 



In the oogonium and segmenting oospore of Fucus Farmer and 

 Williams (1896, 1898) described two centrospheres containing granules 

 and arising independently at opposite sides of the nucleus. Strasburger 

 (1897) reported definite centrosomes with asters all through mitosis. 

 In the sporeling he observed appearances indicating the division of the 

 centrosome, and concluded that the latter represents a permanent cell 

 organ. In a very detailed investigation Yamanouchi (1909) demon- 

 strated in the antheridium and oogonium two very definite centrosomes, 

 which appear independently of each other, become surrounded by con- 

 spicuous asters, and occupy the spindle poles during mitosis (Fig. 61, C). 

 He further showed that when the sperm reaches the egg nucleus a new 

 centrosome appears on the nuclear membrane at the point where the 

 sperm enters. 



In Dictyota dichotoma Mottier (1898, 1900) states that in the two 

 divisions in the tetrasporocyte, in at least the first three or four cell 

 generations of the sporeling, and in all the vegetative cells of the tetra- 

 sporic plant curved rod-shaped centrosomes with asters occur at the 

 spindle poles, the two having arisen by the division of one during the 

 early phases of mitosis (Fig. 21, D, E). Williams (1904) further reports 

 that the entrance of the sperm causes a centrosome to appear in the egg 

 cytoplasm. Centrosomes in Nemalion were described by Wolfe (1904). 



In Polysiphonia violacea (Yamanouchi 1906) there are present during 

 the prophases of every mitosis two centrosome-like bodies in the kino- 

 plasm at opposite sides of the nucleus. A little later the small bodies 

 disappear, while the kinoplasm takes the form of two large centrosphere- 

 like structures (Fig. 21, C); during the later stages of mitosis these fade 

 from view. Yamanouchi believes that these structures do not represent 

 permanent cell organs, but are formed de novo at the beginning of each 

 mitosis. Somewhat similar temporary centrospheres, with radiations 

 but no centrosomes, are present in the tetrasporocyte of Corallina (Davis 

 1898; Yamanouchi). 



Fungi. Among the fungi the best known centrosomes are those of the 

 Ascomycetes (Fig. 22). Harper (1895, 1897, 1899, 1905) described granu- 

 lar disc-shaped centrospheres surrounded by asters at the poles of the 

 spindle in the asci of Peziza, Ascobolus, Erysiphe, Lachnea, Phyllactinia, 

 and other genera. He regarded them as permanent organs of the cell. 

 In a recent paper (1919) he speaks of the ascomycete centrosome as a 

 structure differentiated "as a region of connection between nucleus and 

 cytoplasm and for the formation of fibrillar kinoplasm." Harper be- 

 lieved the ascospore walls to be formed by the lateral fusion of the curved 

 astral rays focussing upon the centrosome, a point disputed by Faull 

 (1905) and others. Centrosomes in additional genera were figured by 

 Guilliermond (1904, 1905). InGallactinia succosa (Marie 1905; Guillier- 

 mond 1911) a single centrosome, which arises within the nucleus with a 



