35 



and from which tlie fertile mud is raked out at stated intervals to 

 spread over the land. From the close resemblance of this germ to 

 Ps. camjjesfris, the cause of brown rot in the cabbage, it is probable 

 that, like the latter, the hyacinth germ is able to live for a long time 

 in the soil of infected fields. 



Diseased bulbs should be burned or put into a jar pf dilute crude 

 sulphuric acid, to which more acid is added from time to time. They 

 should never be thrown into the canals or on waste land, nor should 

 they be allowed to rot in place, for in this way all the soil would 

 finally become infected. Land on which the disease is present should 

 be used for other plants. 



As suggested by Wakker, new varieties should be originated only by 

 hand pollination, both parents being selected from such varieties as are 

 naturally free from this disease, or which are at least little subject to it. 



In concluding these remarks on pathogenesis it may be well to call 

 special attention to certain features of this disease which seem espe- 

 cially instructive. The peculiarities which have impressed me most 

 are: (1) The extremely slow progress of the symptoms — a slowness 

 which is very remarkable if we compare it with the rapid action of 

 such bacterial diseases as pear blight {Bacillus anujlovorus) or the 

 wet white rot of hyacinths which attacked some of my plants in 1898. 

 (2) The extent to which the disease is restricted to the particular 

 vascular bundles which are first invaded, i. e., the very slow invasion 

 of the parenchyma and of remoter vascular bundles protected hy this 

 parenchyma. 



This disease is not only peculiarly a vascular trouble, as Wakker 

 pointed out, but is so restricted to the bundles first invaded that it 

 seems to me impossible that there should ever be anj^ general infec- 

 tion of the bulb scales until after the vessels which form a network 

 in the plateau have become diseased. The disease was not observed 

 in the roots. 



The conditions under which this organism can grow parasitically 

 appear to be narrowly restricted. It is not known to occur on any 

 other host plant. It is a feeble, slow acting parasite and probablj' it 

 would be confined to the domain of pure saprophj^tism were it not 

 for the aeration and other peculiarly favorable conditions occurring in 

 the vascular bundles of the hyacinth. The parenchyma of the bulb 

 scales is distinctly acid and plainly unfavorable to its growth, most 

 likel.v on account of this acidity, since studies of the organism in a 

 variety of culture media have shown it to be peculiarly sensitive to 

 the presence of acids, even those of tlie hyacinth (see Bulletin 28). 



If the parench^'matic tissues of the hyacinth were less acid, if the 

 germ were a more c()i)ious alkali produciM-, if it were less strictly 

 aerobic, if it destroyed cell walls more readily, or finally, if it exerted 

 a more powerful diastatic action on starch, it would, in my opinion, be 

 a much more active parasite. 



