STEUOTURE AND DEVELOPMENT. 65 



normal plants, and in many instances tlie first whorl 

 of the primary stem bore oospores. The different 

 phases of germination in these unimpregnated oospores 

 are exactly like those in the sexually produced 

 oospores of other species. Of the actual occurrence 

 of parthenogenesis in this plant no shadow of doubt 

 can exist." 



Hybridity has been very rarely observed among 

 the Charophytes, and no instances have, we believe, 

 been recorded among the Nitellese. Among the 

 GharesB one instance has come under our personal 

 notice, that of a plant from Hickling Broad and its 

 adjacent Sounds. This was in the first place referred 

 to Gliara papillosa, but further observations have 

 led to the conclusion that it is a hybrid between 

 G. hispida and G. contraria. In Prance Professor Hy 

 has described a hj^brid between G. connivens and 

 G. fragilis. These are the only cases which to out 

 knowledge have been placed on record, but no doubt 

 if careful search is made in pieces of water where 

 allied species are growing together other cases may 

 come to light. No attempt so far as we know has 

 yet been made to produce artificial hybrids. 



The cells of which a Charophyte is com- 

 structure po^ed are much larger than those of 

 cyclosis etc. ™ost other plants, the single cells form- 

 ing the internodes of the stem in some 

 cases attaining to the extraordinary length of 20 cm. 

 There is a considerable difference in the thickness of 

 the cell- wall in different species. 



Bach cell has originally a single nucleus, the 

 nuclear division preparatory to the formation of fresh 

 cells taking place by regular karyokinesis. The long 

 internodal cells ultimately however possess a number of 



VOL. I. 5 



