128 BRITISH CHAROPHYTA. 



or twice furcate into 4-6 rays, those of the upper 

 usually once furcate into about 5 rays, or simple. 

 Oogonia and antheridia enveloped in thin mucus, 

 occurring on the primary branchlets at the second, 

 third, and more rarely at the first forkings, and some- 

 times also on the accessory branchlets. Oogonia soli- 

 tary c. 600-625 ju, long, 375-400 fi broad ; spiral cells 

 showing 9-10 convolutions ; coronula c. 45 /a high, per- 

 sistent. Oospore (unripe) brown, decidedly flattened; 

 outer membrane thin, flexible, and translucent, bright 

 or dull-yellow, brown, obscurely reticulate (PL V, f. 7). 

 Antheridium 350-425 /x in diameter. 



Distribution. — West Cornwall, Looe Pool, near 

 Helston (G. B. B.-W., 1898). 



First record: Journ. Bot. 1898. 



Outside the British Isles N. hyalina, though rare, 

 has a very wide distribution, having been found in 

 Finland, Spain, France, Holland, Germany, Switzer- 

 land, Austria, and Italy; also in Southern Asia, 

 Japan, North and South Africa, North America, and 

 Australasia. 



A medium-sized plant about 15-30 cm. high, the upper 

 whorls forming densely-crowded heads. The larger and more 

 diffuse form, which is that occurring in England, is extremely 

 graceful. It is at once distinguishable from all other European 

 species by the presence of the accessory branchlets, which, 

 being shorter than the primary branchlets, are very noticeable. 



Prof. Ernst has made a careful study of the origin and 

 development of these accessory branchlets, the results of 

 which are published in his memoir (I.e.) ' Die Stipularblatter 

 von Nitella hyalina (DC.) Ag.' 



The ripe oospore, which we have not seen from this country, 

 is about 350 fx long and 300 n broad, usually reddish-brown, 

 and 200 ju thick, and shows 7-8 low, inconspicuous ridges. 



JV. hyalina, N. gracilis, and N. hatrachosperma belong to 

 the group having granulated decoration of the membrane. 

 Of these N. hatrachosperma is the finest grained, N. hyalina 

 stands next in order, while N. gracilis has the largest grains. 

 The granulation in all three species is exceedingly minute, 

 the grains varying from 1-2 fx in diameter. 



