SECT. I 



MORPHOLOGY 



spindle (Fig. 90) agrees in structure with the spindle of more highly organised 

 plants, and so do the processes of division and the formation of the daughter 

 nuclei. The kiuoplasmic radiations round the centrosome-like structures only 

 persist during the karyokinesis. In other similar cases, as in the marine alga 

 Stypocaulon, the correspondence of the body visible in the midst of the radiations 

 during karyokinesis with animal centrosomes has been recently questioned (•''**). 



— -ws-^A-s^": 







ly. 





org^v; 









..^ 





>-<^Ml 



-^ 



/ 



Fi(!. 89. — A nucleus of a young plant of the 

 Brown Seaweed, Fuc^is serratus, piepar- 

 ing to divide. The two centrioles (c), 

 which have arisen by the division of a 

 single one, have already sejiarated from 

 one another ; kp, radiations of the kino- 

 plasm ; s, chromosomes ; n, nucleolus. 

 (X 1000.) 



Fin. 90. — A nuclear spindle of a cell of a young 

 plant of the Brown Seaweed, Fueiis serratus, with 

 split chromosomes in the nuclear plate. c,centro- 

 some-like structures ; kp, radiations of kino- 

 plasm ; sp, spindle fibres ; s, longitudinally 

 divided chromosomes forming the nuclear 

 plate. (xlOOO.) 



They also increase in number by division and form permanent constituents of the 

 protoplasts. Nevertheless the plasmatic masses in Fungi and Bryophyta, which 

 do not contain centrosome-like bodies, appear to arise during karyokinesis at the 

 poles of the nucleus and not to persist after the division. 



The fundamental ditference between the typical and somatic 

 nuclear division and the reduction division may be made clearer by 



B 



Fic. 91. — Diagrammatic representation of ordinary nuclear division (A) and of the reduction 



division (B). 



means of a diagram. Fig. 91 A represents a somatic division with 

 longitudinal splitting of the chromosomes. In A a six longitudinally 

 split chromosomes, distinguished by the different shading, are shown 

 arranged to form the nuclear plate. The two middle ones are seen 

 from the end, the others from the side. In A h the separated halves of 



