Excerpt a Botanica. 



257 



Two specimens of this beautiful insect were brought from Monte 

 Video by Mr. Darwin. 



Baripus rivalis (Molops rivalis, Germar), Dejean. Species Gen. 

 des Col., vol. iii. p. 25. 



Two specimens of this species from Monte Video, and one speci- 

 men from Maldonado La Plata, occur in the collection. 



XXIX. — Excerpta Botanica, or abridged Extracts translated 

 from the Foreign Journals, illustrative of, or connected with, 

 the Botany of Great Britain. By W. A. Leighton, Esq., 

 B.A., F.B.S.E., &c. 



No. 3. On the Structure of the Hairs on the Pericarp of cer- 

 tain Plants. By M. Decaisne. (Ann. des Sc. Nat. n. s. 

 xii. p. 251.) 



One of the characters of the genus Ruckeria is, that of 

 having the pericarp covered with papillae. These papillae, 

 when attentively examined in a dry state, are found to be of 

 a club-shaped form, of a pearly appearance, and with a lon- 

 gitudinal line dividing them into two equal portions. Their 

 base is dilated or curved, in the different species, so as to rest 

 upon one of the cellules of the epidermis, in the organisation 

 of which there is nothing unusual. On placing some of these 

 papillae or hairs in a drop of water, we immediately see them 

 separate at the apex into two lips, and thence emit two tubes 

 (boyaux) of a mucilaginous substance, which issues forth 

 like wires spirally unrolling themselves, twisting about on 

 themselves many times, and finally greatly exceeding in 

 length the hairs into which they were apparently thrust. 



These tubes are apparently formed by a very considerable 

 number of filaments, united and placed one upon the other, 

 in the manner of a skein of thread, of which the pieces adhered 

 together by means of some gummy substance. When these 

 hairs are moistened, we distinguish through their parietes in 

 each of the two lateral moieties, two bodies more opake, at- 

 tenuated at both ends, and exhibiting striae arranged in a 

 regular series, but changing their direction at certain intervals. 



If the hair, instead of adhering to the pericarp, as in the 

 preceding example, is broken oft' at the base, the emission of 

 the tubes takes place at that extremity, and the two are then 

 seen to descend slowly, and to proceed parallel to each other 

 for a short time in unrolling themselves, but afterwards to 

 curve and twist one around the other in an irregular manner. 



Sometimes when the hair is not broken off, the tube issues 

 forth from the side, and almost constantly about the middle, 



Ann. Mag. Nat. Hist. Dec. 1 840. s 



