F. Børgesen: Rhodophyceæ of the Danish VV. Indies. 



349 



each other while in the other species of Martensia this arrangement 

 is not found at all or at any rate only slightly indicated. 



According to Svedelius the coherent tissue of the young frond 

 is formed by filaments congenitally connate just as in the case of 

 the other Delesseriaceæ . Later on intercalary cell-divisions contri- 

 bute to the growth of the tissue. When the coherent tissue has reached 

 a certain breadth the development of the net begins. Some large 

 cells, becoming the basal ones of the net, are formed along the 

 margin and from each of these a row of cells grow up; these cell 

 rows are mutually free with the exception of the uppermost cells 

 of the rows which 

 at both sides all 

 are connected to- 

 gether with those 

 of the neighbour 

 cell-rows. From 

 these connected 

 cells the next belt 

 of coherent tissue 

 originates (comp. 

 Fig.345).Thefiee 

 rows of cells are 

 running nearly 

 parallel to each other; their cells are soon divided by horizontal 

 walls (lying in the plane of the thallus), the cell-rows herewith 

 being transformed into lamellæ. In this way the longitudinal 

 beams of the net are formed. About the same time when divi- 

 sion of the cells takes place in the longitudinal rows of cells 

 the cross-beams of the net begin to grow out. In Martensia Pa- 

 vonia these are formed in such a way that a cell in the longitudinal 

 cell-row grows out unilaterally in the direction of the neighbour cell- 

 row (comp, the fig. 33 of Svedelius). This outgrowth, being separated 

 from the mother cell by a wall, soon reaches the opposite cell-row 

 and then grows together with it in a way very similar to that found 

 e. g. in Dictyurus, Microdictyon etc. In forming the cross-beams in 

 this way Martensia Pavonia differs for instance from Martensia fra- 

 gilis in which two outgrowths issue oppositely from each cell ; these 

 outgrowths meet those issued from the neighbour cell-rows half-way 

 and grow together conjointly. 



Fig. 344. 



. .^ Martensia Pavonia J. Ag. 



Part of the coherent tissue with groups of rhizoids 



issued from the margin. 



(About 80:1). 



