ftH 



DISEASES OF WHEAT. 



house, all (lie plants known to me as having been brought alive from the tropic have in- 

 troduced certain eutophytes peculiar eoch to its species of plants, and not belonging to this 

 country. The great idea of De Candolle, " the spreading of the species of brand depends 

 on the sowing of the spores," since the beautiful observations which Gleichen published 

 more than sixty years ago, can no more be doubted. This great German natural historian 

 found indeed that the wheat crop strewn and sown with brand dust gave over 50 per cent 

 of ears affected by brand, while the dry and thoroughly washed seed exhibited scarcely any 

 ears affected by brand. 



Besides many eutophytes may be transported ; and in the kinds of brand of grain we 

 are by no means justified in denying the transmission by spores, and especially as no hus- 

 bandman can maintain *' that he has cultivated wholly clean seed containing not a single 

 brand-spore," for in practice the extraordinary minuteness of the brand-spores lays an 

 insurmoimtable obstacle in the way of all observations. The parasites which have their 

 abode in the dead parts of plants may easily be propagated by the sowing of their spores ; 

 and a careful observer may in this latter case readily follow the germ of the spores sown, 

 and the gradual development of the parasite through all the stages of its formation, as I 

 have already many times shown in other places. But a multitude of eutophytes, besides 

 the sowing by spores, also require peculiar conditions of soil and a moist atmosphere for 

 their development ; since otherwise the mother plant is not capable of furnishing the nu- 

 trition indispensable for its development, or to perform the secretion of the same from its 

 own fluids. 



These organic processes necessary to such formations are yet partially mysteries to 

 natural historians, which may not be laid open by logical phrases, or such as belong to 

 natural philosophy. Only direct observations can here determine ; and all views, opinions, 

 belief, ond so-called experience are positively injurious, while they are almost ever wanting 

 in any strong induction, and under critical examination sink into their originiil nothingness. 

 It is therefore the wiser openly to admit that we have not yet observed the direct propaga- 

 tion of the kinds of brand by spores ; as we must allow, on a critical investigation of all 

 circumstances, " that the conditions of soil, the influence of cultivation, weather, situation and 

 manure which is required for the spreading of the various species of brand, are not fully 

 known." Such conclusions are more salutary for the advancement of human knowledge, 

 than all the so-called learned or purely empirical talk. 



But since Ehrenberg has practically demonstrated the propagation of the infusoria by 

 eggs and division, and I have also the sowing of fungi and mushrooms by spores, we may 

 loo hope for a similar proof of the propagation of eutophytes by spores, and until then set 

 aside all speculations on their spoiuaneous generation as injurious and unnecessary; and 

 the more so, as nearly every kind of plant has parasites exclusively having their abode in 

 it, and likewise the soil equally necessary to its development. 



