1917] DUNN—DUMONTIA 459 



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f 









cell, and no nucleus is then present in the filament. There are, 

 however, two widely separated nuclei in the auxiliary cell itself, and 

 one of these lies quite near the point of fusion of the filament and 

 the cell. The sporogenous nucleus in Dudresnaya pur pur if era , D. 

 coccinea, and Dumontia filiformis at no time even closely approaches 

 the original auxiliary cell nucleus. The 2 nuclei in all 3 species lie 

 at almost opposite ends of the cell. The carpospores are budded 

 off from that end of the auxiliary cell which contains the sporog- 

 enous nucleus. In Dumontia the original auxiliary cell nucleus 

 and the descendant of the sporogenous nucleus could be identified 

 in nearly all the auxiliary cells which bore carpospores. Oltmanns 

 (9) observed in Gloeosiphonia and Dudresnaya several cases of 

 " blind fusion" where, although a sporogenous filament had fused 

 with an auxiliary cell, no nucleus had passed over and the auxiliary 

 cell contained only its own nucleus. No examples of "blind fusion " 

 were found in Dumontia. It would seem that Oltmanns' state- 

 ment that it is a daughter of the sporogenous nucleus in Gloeosi- 

 phonia which moves into the pericentral cell might be questioned. 

 The two daughters of the auxiliary cell nucleus and the sporogenous 

 nucleus always lie close together. One of these 3 nuclei divides 

 and one of the daughters moves into the pericentral cell. In 

 Dudresnaya purpurifera, D. coccinea, and Dumontia there can be no 

 question as to the origin of the nuclei in the carpospore. They are 

 derived from the sporogenous nucleus. 



Summary 



Dumontia filiformis, during May, June, and the first half of 

 July, grows in abundance in the tide pools and on the bed rock at 

 South Harpswell, Maine. This alga became established on the 



iouth Harpswell between 1905 and 19 13. Antheridial, 



cystocarpic, am 



size and vegetative structure. The average size of the antheridial 

 plants is a little less than that of the other plants. Cystocarpic 

 and tetrasporic plants are found growing together on the same rock 

 and in the same tide pools. Female plants which bear mature 

 cystocarps are easily recognized by the protrusions which these 



orm 



typ 







