324 



broader leaves of the already mentioned specimens from Val- 

 lanes, Iceland. 



The venation is very simple. In the broader leaves three 

 or five veins, in most of the narrow leaves only a single one, 

 while in others and in transition-forms three or one with lateral 

 veins only in the upper part of the leaf, generally making a 

 sharp curve towards the median vein at the beginning and 

 ending. Sometimes parts of them do not meet, either the 

 middle part or those next to the midvein being absent (fig. 12 C). 



Fig. 14. Apex of the leaf. (X ca. 5). 



a, b Callitriche venia L. c—d Callitriche hamulata Ktz. d upper leaves, e, / lower leaves. 



According to Hegelmaier (1864 p. 32) the former are generally 

 formed first, but sometimes the formation of the lateral vein 

 begins in the middle part quite without connection with the 

 mid-vein. 



A few communicating small veins may be found. 



It is remarkable, that the small leaves of С verna terres- 

 trial form, have only one vein, perhaps with a few indistinct 

 branches, the venation of amphibious plants generally obtaining 

 the richest development in emerged leaves. Possibly this is, 

 in one way or another, connected with the form of the leaf. 



Beneath the broad apical pari of the median vein, opening 



