lx PROCEEDINGS OF THE ROYAL HORTICULTURAL SOCIETY. 



of soil, climate, and exposure. Yet deterioration has been complained of 

 in every part where its cultivation is of importance. And the West 

 Indian Agricultural Conference of 1905 seems to agree that it is to be 

 remedied by using seedling canes. 



Another example is the Canadian weed Elodea canadensis, which 

 escaped from a botanical garden in Germany, and at once spread, by 

 vegetative reproduction only, all over temperate Europe. For many 

 years it was a curse to all canals, ponds, lakes, &c., and involved very 

 expensive cleaning : but of recent years, though it is by no means extinct, 

 it is certainly not so serious an evil. In small enclosed ponds, after 

 having been a perfect pest for some years, it suddenly begins to dwindle 

 and may almost totally disappear. A case of this sort came under my 

 own observation in a small pond at the Glasgow Botanical Gardens, 

 where it is now almost extinct, though some five or six years ago it 

 choked the whole of the rest of the vegetation. This case is specially 

 interesting as it is not a cultivated plant, and is one of that hardy band 

 of fresh-water plants which are more widely distributed than any other 

 class of plants known to me. 



A very strong argument in favour of deterioration is the general 

 statistical evidence. Out of some 700,000 flowering plants described, 

 there is not one single case known to me of a plant which does not 

 endeavour to reproduce by seed, although arrangements for vegetative 

 reproduction are exceedingly common. Many plants which we do not, as 

 a rule, look upon as vegetative reproducers habitually form underground 

 stolons, rhizomes, <kc, and are much more rarely formed from seed. 



The answer to the second part of the question is probably a very 

 simple one — old age. However much the method of vegetative 

 reproduction varies, the new plant is merely a part of the old one. A 

 potato grown from a tuber is not a new individual, but a part of the 

 original individual. A close examination of bulbs, conns, rhizomes, 

 suckers, stolons, &c, reveals essentially similar methods of branching, 

 which are made different by the different parts in which the food-store is 

 laid up. The differences, such as they are, have been made much more 

 difficult to understand by the misdirected labours of conscientious 

 botanists. 



That old age is the primary cause I have personally no doubt at all. 

 We know on good evidence (see Bonnier, Traite de Boto.jiique) of trees 

 2.000 years old, not to speak of one kind only, but belonging to several 

 genera. It is not necessary to cite the American mammoth tree of 

 8,300 years, or the Canary Island dragon tree of 10.000 years, which was 

 probably the original of the Greek myth. 



The number of years during which any species can be shown to 

 have been always propagated vegetatively cannot surely be as many as 

 2.000 years, except possibly the sugar-cane and the vine, and in both 

 these cases deterioration has set in. Old age is the reason generally given 

 in both these cases. 



Of course, all cultivated plants are grown under quite unnatural 

 conditions. The brilliant sunshine and long, dry season of Chile are 

 quite different from our insular climate. Cultivation under exceptionally 

 favourable conditions must inevitably weaken the constitution of man, 



