ORIGINAL COMMUNICATIONS. 



XII. — Observations on the Diseases of Plants as illustrated hy 

 the Potato Murrain. By Dr. Schleiden. 



[The present memoir, which is here very slightly abridged, to 

 avoid needless repetition and render it more suitable to this 

 Journal, appeared in the form of an appendix to the treatise 

 of which an account has been given in the two previous num- 

 bers. Though the primary subject is in itself scarcely calcu- 

 lated to excite attention after so much has been written on it 

 and is still daily overloading the Continental press, it is of 

 great importance as regards its general bearing on the diseases 

 of plants, and for this reason is submitted to the Society.] 



The general features as well as the especial marks of dis- 

 tinction which are exhibited by the more important diseases to 

 which potatoes are subject, are so extremely various, that it is 

 necessarj' to examine a large quantity of specimens before we 

 can draw up the essential characters of any particular disease, so 

 as to be entirely free from individual and local circumstances. 

 Since the first appearance of the potato-murrain I have paid con- 

 stant attention to the subject, collected all possible information, 

 and carefully examined a great quantity of tubers from all parts 

 of Germany, without however finding any reason to alter the 

 views which I entertained in the year 1845. My prediction that 

 the malady was independent of temporary causes, and that it 

 would never disappear, has, at least at present, been sadly verified. 



1. The following general remarks, which are founded on in- 

 formation derived from various quarters, are of great importance 

 to the due estimation of the nature of the disease. 



And first I must protest against the erroneous notion that the 

 malady is of recent origin. The cultivation of potatoes diffused 

 itself very slowly over Europe, and especially in Germany. From 

 its very first commencement complaints were made of degeneration 

 and disease, which became still louder and more urgent as it ex- 

 tended ; and indeed every one well acquainted with the history of 

 the potato is aware that from the middle of tiie last century, a few 

 years only were free from disease, every succeeding year in general 

 exhibiting some more aggravated and widely extending form. 



