577 



given by Mr. Wilson. I immediately wrote back to my friend, and 

 begged he would at once send me some good plants to cultivate, 

 which he kindly did, and on receiving them I had no difficulty in iden- 

 tifying them with the canal plant. To prove this, as well as to afford 

 others an opportunity of judging for themselves, I had plants from 

 both localities planted together, where they have now been growing 

 upwards of one year, and they continue to bear as much general re- 

 semblance to each other as any two things of the same kind in nature 

 can well do, but you know there are those who go so far as to affirm 

 that no two eggs laid by the same fowl are exactly alike. E, Mackaii 

 and E. arenarium are also growing along with them, each species, or 

 permanent variety, whichever you will, retaining its respective cha- 

 racters without the slightest appearance of altering. In Ireland I 

 have not yet seen intermediate states of either collected by any bota- 

 nist, but the English specimens of E. arenarium from sand-hills at 

 the mouth of the Mersey, appear rather different from the Portmarnock 

 plant, inasmuch as they are considerably larger in all their parts. The 

 Scotch plant from the Sands of Barry is identical with the Portmar- 

 nock one. 



The distinguishing characters which mark the hyemale section of 

 British Equiseta have been so ably detailed in the second edition of 

 the * British Ferns,' that I have nothing new to add to support the 

 opinion of the plants in question being permanently distinct forms of 

 the genus. I may, however, be permitted to ask the natural conclu- 

 sion likely to be arrived at, when we thus find that they occur in lo- 

 calities widely apart, precisely under similar circumstances, retaining 

 all their respective characters, and that they remain unaltered when 

 submitted to the test of cultivation. Surely we cannot think them 

 accidental varieties, nor permanent local varieties, because neither 

 changes of soil or situation essentially affect them. The only remain- 

 ing test, then, to prove them to be what we are in the habit of regard- 

 ing as species, is, to try whether their reproductive organs will perpe- 

 tuate the same forms without any sensible degree of change ; and 

 this, I venture to conjecture, will be the case when fairly tested. I 

 have no wish, as you observe, that any ne\^ name should be added. 

 I am perfectly satisfied now that they are clearly defined, and have 

 no doubt of the correctness of your views in referring the semi-aqua- 

 tic plant to the true E. variegatum of Weber and Mohr. E. arena- 

 rium is probably the best name we could have to distinguish the 



