SPYRIDIACE^. 197 



arranged lengthwise, with horizontal, forked, necklace-like 

 branches, and an outer series consisting of a single row of 

 small cells. Spores in roundish clusters (favellae), formed 

 out of and among the forked branches of the cells of the 

 wall ; tetraspores cruciate, also formed from the cells of the 

 wall, but, of course, in separate plants. — Dumontia, in 

 honour M. Dumont, a French naturalist. 



The species of this genus are widely distributed, chiefly 

 in temperate climates ; only one is found on our coasts. 



Dumontia filiformis. The thread-like Dumontia. 



Fronds varying from an inch to two feet in length, and 

 from one-tenth to half an inch in width ; stem undivided ; 

 branches very long and simple, attenuate at the tip. Spores 

 formed out of the forked cells of the wall of the frond. 



This is a common species, and its characters are well 

 marked and constant. Luxuriant specimens, with very 

 wide fronds, whose branches are variously twisted and 

 waved or frilled, are occasionally found near the mouths 

 of fresh-water streams. This form is mentioned by 

 Dr. Harvey as var. /3. crispata. D. filiformis grows on 

 rocks, etc., in tide-pools during summer, and is annual. 

 Some specimens that I obtained in Jersey a year or two 

 since were proliferous at the tips of the branches. 



Order XIX. SPYRIDIACE^. 



Sed or Srown-red Sea-weeds with a thread-like, jointed, 

 tnonosiphonous frond, more or less coated with small cel- 

 lules. Fructification : — 1. Spores formed in the upper 

 cells of hranched jointed threads, which radiate from a pla- 

 centa enclosed in a cellular pericarp in external concepta- 

 eles ; 2. Tetraspores external on the ramelli. 



