kx PROCEEDINGS OF THE ROYAL HORTICULTURAL SOCIETY. 



b. Economic reasons. (1) Supplanting by varieties of greater 

 productiveness or other desirable quality. (2) Ease with 

 which new varieties are raised. (3) Novelty of later-raised 

 varieties. 



2. But it is also due to inherent causes, (a) Old age or disturb- 

 ance in the balance between waste and repair, (b) Possibly 

 the tendency to form seed, but there is a marked exception in 

 the ' Ashleaf.' (c) The potato is an exotic, and is, therefore, 

 never grown under absolutely natural conditions. It may be 

 that even after 300 years' cultivation it has not become 

 completely adapted to or in harmony with its environment. 



IV. How is the fact that certain varieties (e.g. ' Ashleaf,' ' Early Rose,' 

 ' Magnum Bonum,' ' Maincrop ') do not appear to have degenerated after 

 long cultivation to be explained in view of the foregoing facts ? It is 

 probable that newly raised varieties vary in vigour as well as in other 

 characters, some having sufficient vigour to carry them through only six 

 years, others through very many. Cross -fertilisation, as a rule, results 

 in the production of longer-lived varieties than does self -fertilisation. 



V. Points of practical importance. How may the life of a variety be 

 prolonged ? 



1. Greater care should be exercised by raisers in introducing new 



varieties. Only those with plenty of initial vigour should be 

 offered to the public. 



2. Well-matured tubers should be chosen for " seed." Size of 



seed is not so important, but uncut tubers of medium size 

 give, in the long run, the best results. 



3. Selection of tubers in other directions can be expected to give 



but little result; "sports" do occasionally occur, but are 

 usually of no practical value. 



4. Sets should be stored so that they do not exhaust themselves 



by premature sprouting. 



5. The seed should be frequently changed ; the best seems to come 



from Scotland, but even there change of soil seems necessary. 

 The second year's crop is usually the best. 



6. Probably excessive manuring with nitrogenous manures may 



lead to more rapid degeneration. 



VI. The main objections to the idea of degeneration naturally 

 occurring in asexually produced varieties were (1) the fact that some 

 varieties persist apparently unchanged for long periods — this point is 

 dealt with in paragraph IV. ; and (2) the idea that plants produced 

 asexually are entirely new individuals, and not merely parts of one 

 individual ; this question cannot be regarded as definitely settled. 



VII. Other points. The discussion also brought out a considerable 

 body of facts regarding other plants, of great use and interest, and provided 

 suggestions for a very large amount of experimental research. 



Etherisation of Plants. — Professor Johannsen, of Copenhagen, the 

 inventor of the process, gave a short account of the method of etherising 

 plants in order to shorten their period of rest and induce them to flower 



