K.— BOTANY. 203 



realise that they would both repay carefully arranged cultural and 

 cytological research. 



In the case of Rubus also it seems likely that carefully controlled experi- 

 ments would possibly reveal the fact that habitat or hybridisation, rather 

 than a ' fixed ' type, was the raison d'etre of several ' species ' now immor- 

 talised in the Index Kewensis. Whatever research may reveal in these 

 genera, it has been shown in Centaurea,^" as the result of careful genetical 

 experiments, that at least three described ' species ' are of hybrid nature 

 or origin, for exact counterparts of Centaurea jutigens Gugl., C. pratensis 

 Thmll. and C. Drucei C. E. Britt., have been artificially produced by 

 Marsden- Jones and Turrill at Potterne, and have been proved either to be 

 hybrids or segregates from hybrids. It is evident also that some half- 

 dozen other ' species ' of Centaurea will have to be similarly reduced in 

 the course of the next year or two, when the experimental investigations 

 have been completed. From this work, and from similar experiments with 

 Silene maritima and S. vulgaris, ^'^ it seems evident that hybridisation is 

 common in the wild flora of Britain, and that ' hybrid swarms ' occur, 

 comparable to those to which Lotsy has called attention in South Africa, 

 and Cockayne and Allan have demonstrated so clearly in the New Zealand 

 flora. 



In dealing with intra-specific variation within a polymorphic ' Linneon,' 

 such as Silene maritima, Marsden-Jones and Turrill have wisely refrained 

 from coining a number of new names, but have attempted to formulate a 

 scheme comparable with chemical symbolism, which should prove of con- 

 siderable assistance to botanists who are confronted with similar difficulties 

 in other groups of plants showing similar polymorphism. 



An important development, arising out of the more intensive study of 

 wild species and possible hybrids and the associated genetical work and 

 controlled cultivation, which is so pregnant of far-reaching results, is the 

 need of greatly extended Herbarium records and field notes. For genetical 

 work to be of permanent value it is essential that ample material of the 

 parent plants and their oft'spring should be preserved for reference, and in 

 the case of assumed wild hybrids, representative specimens of the parents 

 and of all the linking forms are required. 



I am glad to say that at Kew we have now established special ' herbaria ' 

 for genetical specimens and for hybrids, where specimens forming as 

 complete a set as possible are kept together, apart from the General 

 Herbarium collection. ^^ At present it is fairly rich in certain groups of 

 New Zealand hybrids, thanks to the kindness of Dr. Cockayne and his 

 associates in the Dominion. We also have a very full set of specimens 

 from the plants which are being used in our transplant experiments, 

 which exhibit clearly all the changes which so far have been recorded. 

 There is also a good series of mounted sheets showing the hybrid forms of 

 Centaurea, Silene, Saxifraga potternensis, &c., which have been produced 

 under controlled experimental conditions, together with a collection of 

 similar ' forms ' which have been discovered in the wild condition. 



'" See Gardeners' Chronicle, March 15, 1930, p. 210. 



>i Kew Bulletin, 1929, pp. 145-175. 



^2 See Kew Bulletin, Appendix I. 1929, p. 42 ; 1930, p. 40. 



