THE DEVELOPMENT OF DUMONTIA 277 



binucleate tetrasporangia would indicate that mitosis had just 

 taken place. 



Other workers on the Florideae have experienced some diffi- 

 culty in obtaining stages of mitosis. Lewis reported that practi- 

 cally no mitotic figures were found in material which was kept in 

 running water in the laboratory and fixed at every hour. He 

 did, however, succeed in finding the desired stages in material 

 which he fixed in the field. If Lewis' figures show all the im- 

 portant stages in mitosis as it occurs in the tetrasporangium 

 nucleus in Griffithsia, the process is not exactly similar to the 

 reduction division which occurs in most plants. No spireme 

 was seen in any nuclear divisions in Griffithsia. Svedelius 

 carefully worked out mitosis in the tetrasporangium of Deles- 

 seria and failed to find a spireme. He found later in studying 

 tetraspore formation in Nitophyllum that the spireme in this 

 form is very delicate and of short duration. Svedelius believes 

 that he may have overlooked the spireme in Delesseria. It is 

 conceivable that mitosis in the Florideae is quite similar to 

 that in the higher plants; but in many of the forms it has not 

 been possible thus far with our present technique to detect all 

 the stages, some of which may be of short duration. 



. The nuclear and cell division. The nucleus in the tetrasporan- 

 gium is spherical when it first assumes a central position in the 

 cell. The nucleus elongates in preparation for division (fig. l,K). 

 All the chromatin is still in the nucleolus at this stage and the 

 linin network is also present. In the next later stage, the 

 nucleus has assumed a spindle shape. No network is now pres- 

 ent and no spindle fibres can be definitely made out, although 

 there is a slight suggestion of the latter. It is difficult to de- 

 termine the structure of the chi-omatin mass because it stains 



chromatophores. X 700. F, G. Nuclei of mother cells of tetrasporangia, show- 

 ing vacuoles in nucleoli, and linin fibrillae. X 1000. H. Longitudinal section 

 through tetrasporangium, showing position and structure of chromatophores. 

 X 700. /. Longitudinal section through tetrasporangium, showing jacket of 

 sterile cells, and structure of nucleus. X 700. ./. Longitudinal section of tetra- 

 sporangium showing cytoplasmic net, peripheral chromatophores, cytoplasmic 

 jacket enveloping the nucleus and protein granules. X 700. K. Nucleus elon- 

 gating in preparation for division. X 1000. 



