92 BRITISH CHAROPHYTA. 



KEY TO THE BRITISH SPECIES. 



NITELLA. 



Ultimate rays of branchlets one-celled. Coronula 



deciduous. 



Antheridia and oogonia enveloped in mucus. Ridges 

 of oospore very prominent. Dioecious 



1. N. capillaris. 



Antheridia and oogonia not enveloped in mucus. 

 Ridges of oospore not prominent. Dioecious or 

 monoecious. 



Dioecious. Oospore 375-425 /x long . . 2. N. opaca. 

 Monoecious. Oospore 500-5 75 /m long. 



Branchlets 6-8 in a whorl . . 3. N. flexilis. 



*J 



Branchlets 1-3 developed in a whorl 



4. N. spanioclema. 

 Ultimate rays 2-3-celled. Coronula persistent. 



Branchlets in each whorl uniform and in one series. 

 Branchlets once furcate. Secondary rays usually 



minute and inconspicuous . . 5. N. translucens. 

 Branchlets twice to four times furcate. Ultimate 



rays not much shorter than the penultimate. 

 Penultimate cell of terminal ray rounded at the 

 apex. Apical .cell minute. Ultimate rays 

 usually all 2-celled . 6. N. mucronata (type). 

 Penultimate cell of terminal ray tapering at the 

 apex, which is not much broader than the 

 base of the apical cell. 



Ultimate rays, some 2-celled, some 3-celled. 

 Membrane reticulate 



6. N. mucronata var. gracillima. 

 Membrane granulate . . 7. N. gracilis. 

 Ultimate rays all 2-celled. 



Oogonia produced at the first furcation of 

 the branchlet. Membrane granulate 



8. N. batrachosperma. 



Oogonia not produced at the first furcation 

 of the branchlet. Membrane reticulate 



9. JV. tenuissima. 



Branchlets in each whorl of two kinds, smaller 

 accessory branchlets being produced above and 

 below the primary branchlets . . 10. JV. hyalina. 



