137 



tions which Meyer had enumerated respecting this phaeno- 

 menon may be explained in a different sense, and in fact more 

 in accordance with nature, if we start from the general point of 

 view, by the periodical occurrence of sleep, which appears to 

 be common to all animated beings. M. Dassen placed a pot 

 containing Impatiens noli tangere during the night in a dark 

 place, and the result was, that the leaves even during the fol- 

 lowing day retained the same direction. Another plant was 

 placed during the day-time in a dark place, and for two entire 

 days the leaves retained the usual direction which is proper 

 to them in the daytime. From these and other experiments 

 M. Dassen concludes that the motions of plants without 

 swellings are caused solely by the process of vegetation, and 

 that this is rendered evident as soon as the leaves are exposed 

 to unnatural external influences. 



I ask then, whether from the examples cited the phaeno- 

 menon of vegetable sleep can be denied ? On the contrary, 

 phaenomena exactly similar may be proved to exist in ani- 

 mals. 



Diseases of Plants. 



I have published some observations on the development of 

 smut in maize*, which demonstrate the origin of this incu- 

 rable disease in the interior of the cells of the affected part. I 

 consider it to be a settled fact, that the smut (Ustilago, Link,) 

 is not a contagious disease, but is inherited, and arises from 

 the stoppage of the saps produced by superabundant manure 

 foreign to the nature of the plant. At one or at several places 

 of the inner surface of the affected cells small deposits of mucus 

 are formed, from which filiform ramified bodies proceed, which 

 are colourless and almost transparent, but contain a quantity 

 of small molecules consisting of a somewhat more solid sub- 

 stance. These mucous filaments, in the interior of the cells, 

 soon present constrictions at various places, first generally at 

 the apices of the small lateral branches ; and these constricted 

 ends take an ellipsoidal and lastly a spherical form, become of 

 a yellow colour, and change into those minute brown vesicles 

 of which the smut consists. The destruction of the cellular 

 walls by dissolution commences with the aggregation of these 



Wiegmann's Archiv for 1837, p. 419. 



