Excerpta 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 
thecommon Groundsel (Senecio vulgaris, 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- 
nacee. By M.J. Scuierpen. (Linnea, 1839, iv. p. 385.) 
SCHLEIDEN purposes to publish a Monograph of the Lem- 
nacee, 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.—Ep.] 
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