Excerpt a Botanica. 259 



Note. — With a view of connecting the above with British 

 Botany, it may be proper to remark, that I have observed a 

 phenomenon similar to that described above as existing in 

 the genus Ruckeria, in the hairs which clothe the achenia of 

 the common Groundsel (Senecio vulgar is, Linn.)*. Theachenia 

 should be collected on a dry day, when fully matured, and 

 before they have been wetted either by dew or rain. On 

 placing them under the microscope, the silky hairs will be 

 found to be very much adpressed and scarcely conspicuous. 

 Immediately, however, on the application of a drop of water, 

 the hairs become prominent and erecto-patulous, and will be 

 perceived to be in form linear, emarginate or notched at the 

 apex, having a darker longitudinal line communicating with 

 the notched apex, and thus as it were dividing the hair into 

 two cylindrical but attached tubes. On the continued ap- 

 plication of the water for a short time, a spiral coil encircling 

 a mucilaginous substance issues from each of the segments of 

 the apex, and after twisting upon itself several times, becomes 

 at length quiescent, extended in a nearly straight direction, 

 and considerably longer than the hair from which it pro- 

 ceeded. — W. A. L. 



Shrewsbury, Oct 16, 1840. 



No. 4. Conspectus of the Genera and Species of the Lem- 

 naceae. By M.J. Schleiden. (Linnaea, 1839, iv. p. 385.) 



Schleiden purposes to publish a Monograph of the Lem- 

 nacece, founded on the results of a continued study of the 

 plants during five years, aided by the experience of his uncle 

 Horkel, a very skilful investigator of the tribe. In the mean 

 time he presents the following as a Prodromus of his intended 

 work. 



According to his observations these plants do not flower 

 seldomer than other proliferous Phanerogama ; the rarity of 

 their detection in that state is consequently owing to our re- 

 searches being conducted unadvisedly or at an unseasonable 

 period. He has frequently examined in a complete state Lemna 

 minor, trisulca, and gibba through all the stages of the deve- 

 lopment of their flowers, fruits, and germination. 



In the arrangement of the genera, he has generally followed 

 the principles so successfully applied by Schott, and later by 



* [The structure and property of the hairs on the achenia of this plant 

 have been previously observed by Mr. Brown. — Ed.] 



s 2 



