-—■ 



TM. Foslie. Isthmoplea, rupincola, a new Ålga, 



131 



on the contrary, most of ten only one of the cells give ris* 

 to a sporangium, and even in most cases, when the cell in 

 a monosiphonous part of a branch is divided by two longL 

 tudinal walls into three cells, only one sporangium or branch 

 is developed from one of the outer cells, or sometimes one 

 sporangium from the outer and one from the middle cell. 

 Therefore, the sporangia are irregularly scattered in the 

 branches as well as in the main axis, rather seldom opposi- 

 te to one another or opposite to a branch. I have not found 

 the sporangia whorled, but they often appear in pairs from 

 adjacent cells in adjacent segments, or side by side with a 

 branch, or alternately opposite to one another or to a branch 

 in two adjacent segments. I have also seen a cell of a 

 branch divided by a longitudinal wall into two cells. the 

 one giving rise to a branch, or not, and the other again di- 

 vided by an oblique wall in trans verse direction into two 

 cells, and then the one of these developed itself to a spo- 

 rangium. Besides I have seen a sporangium divided by a 

 longitudinal wall into two daughter cells, and twice I found 

 sporangia rising from a monosiphonous part of a branch 

 ■ without any earlier cell-division like the development of the 

 sporangia in Ectocarpus. 



* 



The sporangia are roundish, agreeing in shape with 

 those in I. sphærophora, but they are only 28 — 40 (x thick. 



L rupincola was, when collected at the beginning of 

 August, richly provided with young as well as ripe sporan- 

 gia, or emptied ones. 



Tromsø 14. XI. 1891. 







