EXPLANATIONS OF THE CATALOGUE. 
3 
On Salix Mr. J. Fraser writes : 
“The list of Salices is alphabetical throughout as to parentage. The secondary 
numbers within brackets mean that the trees were either planted, introduced, 
extinct or recorded with doubt. Living plants of S. triandra x vintiutdis look so 
different that I have recorded them under (a) hippopluvfolia and (b) Trcvirani. My 
specimens of the latter have frequently three stamens to a bract of the catkins. I 
have been unable to segregate S. fragilis, and think there is little if anything in the 
female S. fra pit is L. var. brilannica F. B. White. S. alba L. var. ctvrulea (Sm.) is the 
ordinary acceptation of the variety. 1 consider S. purpurea L. f. Lambertiana as 
the stooled or cut down state of the form ; and S. purpurea L. /. Wootgariana 
(Borrer) as the adult of the same plant. I have both forms off the same bush, and 
cultivation also proved it. 1 have given recorded comital numbers for both states, 
but it does not follow that 20+11 would be a correct record of comital numbers 
for .S', purpurea f. Lambertiana. 
S. ferrnginca G. Anderson is recorded as S. ciuerca x viminalis f. Jerruginea 
G. And. because of the very short pubescence and because the leaves are often 
rusty beneath. Wimmer and Dr. F. B. White were of this opinion. 
S. rugosa Leefe I have placed under S. caprea X viminalis with a doubt as 
S. caprea x viminalis f. rugosa (Leefe). 
' 1 have consulted many pub ications for the comital numbers, including 
Linton's Monograph , Dr. White's Revision , the Journal of Botany from 1883-1924, 
Cambridge Brit. Flora, the But. Exchange Reports, and feel confidence in the 
records of Rev. E. F. Linton, Rev. W. R. Linton, Rev. E. S. Marshall, Mr. W. A. 
Shoolbred, Mr. J. G. Baker, Rev. Moyle Rogers, Messrs. Jas. W. White, J. E. Little 
and many other modern and recent collectors. 
The sequence of species in the list is that adopted by the Rev. E. F. Linton in 
his Monograph of the British Willows." 
On Potamogeton Mr. Arthur Bennett writes : 
“ Many more varieties might have been given, but in the present state of the 
study of tlie genus they are better, for the present, anyhow, left out. The death of 
Dr. Hagstri'wi, the Swedish student of the genus, involves a great loss and he is 
very difficult to replace. Our American confreres, however, do not accept all his 
hybrids, etc." 
On Charophyta Mr. James Groves and the Rev. G. R. Bullock-Webster write : 
“They would wish it to be understood that the varietal names given under 
the more polymorphous species merely represent well-marked extremes of 
variation, and do not therefore imply divergent races.” 
The sequence of the Tenth Edition has in the main been retained though 
drastic alterations in the arrangement of the species have occasionally been majie 
as in the case of the Hieracia, The general order follows Bentham & Hooker's 
Genera Plantarum , also the nomenclature excepting where the rules of priority 
have made a change necessary. 
Most of those who will use this new edition already possess a copy of 
the Tenth Edition, and as the supply of the latter is not yet exhausted copies 
can still be obtained by those desiring them. For these reasons I do not propose 
again to incorporate some of the general information contained in a former 
introduction, but 1 think it may be useful to quote the following notes which 
are equally applicable to the present edition. Sub-species are treated as varieties 
or raised to specific rank and hybrids are placed in alphabetical order as in 
the previous edition, in accordance with Vienna rules. 
The question of the inclusion or rejection of certain aliens from the Catalogue 
is a point that will always involve differences of opinion. The policy adopted in 
the present edition has been in the direction of reducing the number by expunging 
the names of a few species hitherto included that are of very rare or doubtful 
occurrence. Those interested in the subject may be referred to that excellent little 
work, Dunn's Alien Flora of Britain, which has been carefully reviewed and 
commented on in the Journal of Botany, pages 138 and 207, 1906. 
The difficulty of dealing with this matter was felt by the authors of the first 
edition of the London Catalogue, published in 1844, where a list of “Excluded 
Species" was printed on the inside of the buff cover; the Introductions to 
