480 * BOTANICAL GAZETTE [December 



tetraspore mother cell of Dictyota (32, 66). Other algae, such as 

 Corallina (8), Fucus (15, 56, 73), Polysiphonia (71), show highly 

 advanced centrospheres at the poles of the spindle; but investigators 

 claim that in Corallina and Polysiphonia they appear simultaneously 

 at the two poles during prophase, culminate at metaphase, and 

 disappear at anaphase or telophase; and in Fucus one of them 

 appears before the other and they disappear at telophase; only 

 as rare cases they remain recognizable at the side of the resting 

 nucleus. Thus, so far as present knowledge goes, the persistent 

 continuity of polar organization in algae cells has not been demon- 

 strated through successive cell generations. 



The subject of polar organization has received especial atten- 

 tion in Harper's studies on mildews, especially Phyllactinia (18) . 

 In this form, the "central body" lies within the membrane of the 

 resting nucleus, and it is connected with chromatin strands so as 

 to give polarity to the nucleus. The poles of the spindle are 

 formed by division of the central body. Harper believes in the 

 permanence of this structure from mitosis to mitosis, and in the 

 persistence of its connection with chromatin. 



The studies of recent years on the cells of pteridophytes and 

 spermatophytes have failed to support certain claims for the pres- 

 ence of centrosomes and have indicated that their cells are without 

 visible polar organization. Marquette (28) published the view 

 that the presence of polarity in the leaf cell of Isoetes is manifested 

 by a large starch-containing body that lies closely pressed against 

 the side of the nucleus. Previous to nuclear division, according 

 to Marquette, the polar structure divides, and during mitosis 

 the structure persists up to telophase, and finally one of them 

 remains at the side of the newly formed daughter nucleus, and a 

 similar constriction division occurs in the structure previous to the 

 next nuclear division. He also found a polar organization of the 

 spore mother cell of Marsilia, in the form of aggregated starch 

 grains, conspicuous at the time of synapsis, but disappearing just 

 before the formation of the first spindle; the organization is of 

 very short duration, not continuing throughout the mitosis. 



In Cutleria and Aglaozonia, polar organization is manifested 

 by the appearance of centrosome-like structures with or without 



