210 LETTER XLVn. 



of the Crowfoot Tribe often consists, as you know, of 

 a considerable number of little, one-seeded, closed 

 nuts, with an oblique style at the point ; in short, in 

 all these, and some other respects, Alisma is so like a 

 Crowfoot, that it might actually be referred to the 

 tribe of that name by any but a very cautious observer. 

 The principal objection to its being placed in the 

 Crowfoot Tribe, lies here ; it is only now and then in 

 Ranunculaceous plants that the number three occurs, 

 and where it does exist, it is confined to the sepals or 

 the petals, and is not found in the stamens or carpels : 

 but in Alisma it occurs throughout every part ; in the 

 former, therefore, it may be regarded as an occasional 

 deviation from a rule, while in the latter, it must be 

 looked upon as the rule itself. In fact, the seed of 

 Alisma, which in all these cases is the court of final 

 appeal, shews that Alisma, is in reality, an Endogen. 

 If you open one of the nuts, you will find the seed 

 standing erect {fig- 8.), and containing a monocotyle- 

 donous embryo, curved upon itself into the form of 

 a horse-shoe. 



The result of this examination shews how necessary 

 it is, in doubtful points, to weigh and balance every 

 thing that can be observed, and not to decide without 

 the most careful investigation. In this case there was 

 no real difficulty in arriving at the truth ; it was only 

 care and attention that were required. 



The white Water-Lily (Nymphsa alba), although 

 an aquatic like the Alisma, is in some respects very 

 different. I select it as another case where a little 



