352 BACTERIA IN RELATION TO PLANT DISEASES. 



is sufficient and this is perhaps the best method. An extra supply of knives will allow of 

 sterilization without loss of time. For the same reason, in setting out bulbs the greatest care 

 should be exercised not to wound them. 



On May 20, 1883, Wakker removed the foliage from 17 bulbs when the leaves began 

 to show signs of the disease. On September 26, only one of these bulbs was diseased. The 

 other 16 were potted and bloomed the following April, and the bulbs were still sound when 

 re-examined in June. This experiment was repeated by him several times with the same 

 result. It was also tried by some of the Dutch growers with entirely confirmatory results. 

 There can be no doubt, therefore, that early removal of infected leaves will preserve the 

 bulb from infection. This shows very clearly that bulbs are often infected from the leaves. 

 The writer believes that natural infection also takes place through the flower cluster and 

 that insects will be found to be carriers of this disease. 



A clue to the best method of eradicating the disease is afforded by the fact that these 

 plants show a marked difference in susceptibility, some varieties contracting the disease 

 readily and others being entirely or nearly immune, as shown in the remarks under Etiology. 



If we can depend upon the statements respecting susceptibility there is good ground 

 for thinking that many resistant varieties with other desirable qualities might be originated 

 by cross-breeding and selection. The future of hyacinth growing on infected lands in 

 Holland depends to a considerable extent, it would seem, on taking advantage of this fact. 

 I can not think of any better means of eradicating this disease than by the origination of 

 varieties which are not subject to it. This can probably be accomplished by using for 

 one parent hyacinths which are not subject to this disease, and for the other those having 

 other desirable qualities. From their progeny, for continued propagation, should be selected 

 only those kinds which combine resistance to disease with other good qualities. In this way 

 it is likely many resistant varieties of desirable character could be originated, but only at 

 a very great outlay of time and trouble, since it requires about 7 years to grow bulbs from 

 seed to a size suitable for market. The work of originating and fixing desirable strains 

 would probably require several decades and were best done by the Government or by 

 expert propagators, subsidized by the growers. Meanwhile diligent search should be made 

 to know whether it is not possible to reduce the amount of the disease by the discovery 

 and destruction of some insect carrier. 



PECUNIARY LOSSES. 



The writer knows nothing very definite as to the extent of the losses in the Netherlands. 

 His only guide is the general statement of Dr. Wakker that it is one of the most serious 

 diseases of the bulb in Holland, and statements made to him in Holland in 1906. The 

 disease continues to be wide-spread and does much damage every year (p. 341). The 

 majority of the fields are infected and there is no opportunity for shifting to new fields 

 because there is only a small amount of good hyacinth land in Holland, and practically 

 all of this is occupied.* 



HISTORY. 



The disease has been known in Holland for a long time, but Wakker was the first to 

 ascribe it to bacteria. For a full abstract of his papers see American Naturalist, 1896. The 

 most important are in Dutch. No other Dutch writer has done much with the disease. 



"The best soil is a graj sand with a sandy subsoil and the soil-water within a foot of tlie surface. Heavier soils 

 and soils with watei at greater depths are not well adapted to the hyacinth. 



