Timherlake — Swarm-Spores of Ilydrodlctyon. 513 



is not to be considered in any way more primitive than tlie or- 

 dinary type of nucleus found in other thallophytes and the 

 higher phmts. The existence of a body so closely resembling 

 a centrosome in Hydrodictyon is in accord with the facts as 

 worked out in other lower forms, especially among the Fungi 

 and broT\Ti Algae. 



The significance of the variation in size of the nuclei is not 

 at all clear. The very large nuclei probably represent cases 

 of unusual growth of the smaller ones. Such a variation in 

 size of the nuclei is not uncommon in other plants at diffcTent 

 stages of the life history. For example, in the uninucleate 

 plant of Syncliitrhtm the nucleus is many times as large as the 

 nuclei of the multinucleate staore or the sin<]^le nuclei of the 

 spores. The striking fact in Hydrodictyon is, however, that 

 the very large nuclei may occur in practically any stage in the 



life history. Whether these larsie nuclei give rise to smaller 

 ones by division, as is the case in Syncliitrium, is not clearly 



evident; but the variation in the size of the soindle indicates 



that thev do. 



The question as to whether direct nuclear division takes 

 place in Hydrodictyo}2 is as yet unsettled. While many of 

 the figures indicate quite strongly stages in such division, 

 the evidence is not at all conclusive. As Hertwig very justly 

 remarks, the mere fact that a nucleus may be elongated and 

 constricted in its equatorial region is not to be taken as posi- 

 tive evidence that direct division is in progi'ess, for in many 

 cells the nuclei are capable of assuming a great variety of 

 forms without showing any other indication of division. In 

 Hydrodictyon the capacity of the nuclei to assume such varia- 

 tions in form is very marked and it is quite probable that the 

 elongated nuclei that appear to be constricted in the middle 

 are simply forms of resting nuclei coordinate with the more 

 angular or pointed forms. 



As the facts at present stand, there are two distinct methods 

 of cell division in plant cells, peculiar to the thallophytes on 

 the one hand, and the coi*mophytes on the other. In the 

 former types we have such coenocytic cells as the fungus spor- 

 anges and the Hydrodictyon cell where there is a progressive 



