214 Linnaan Society : — 



Read, in conclusion, an " Extract from a Memoir on the Origin 

 and Development of Vessels in Monocotyledonous and Dicotyledo- 

 nous Plants." By Dr. Francisco Freire Allemao of Rio de Janeiro. 



Dr. Allemao states that in 1849 he commenced a series of micro- 

 scopical observations on several points of vegetable anatomy, and in 

 particular on the origin and development of vessels in the roots of 

 plants. In 1851 he read before the Vellozian Society of Rio de 

 Janeiro a memoir in which the most important facts observed by him 

 were shortly stated, which memoir he revised and published in 1852, 

 as the third of his " Botanical Exercises," in the ' Trabalhos da So- 

 ciedade Velloziana,' p. 101. In the following year he pursued his 

 investigations into the growth of vessels in germinating seeds, and 

 extended them to the next stage in the development both of dicoty- 

 ledonous and monocotyledonous plants. This inquiry is not yet 

 completed, but Dr. Allemao transmits the extract communicated by 

 Mr. Miers, together with a portion of the illustrative drawings, with 

 the view of ascertaining whether his observations are really, as he 

 believes them to be, new to science, and whether they are sufficiently 

 exact. 



The drawings represent first, a young plant of Sida carpinifolia, 

 but little developed, showing the epigeal cotyledons still enveloped 

 in their seminal integuments. The caulicle (radicle) is linear and 

 without ramification. Seen under the microscope the nervures of 

 the cotyledons are found to be composed solely of tracheal vessels, 

 two of which constituting the midrib are continuous with those of 

 the caulicle, which are four in number, distinct, entire, straight, 

 parallel, and equidistant, descending more than half the length of 

 the caulicle, the lower portion of which does not yet exhibit any 

 vessels, nor does its radicular bulb show any tendency to form roots. 

 In a somewhat more developed stage, the nervures of the cotyledons 

 have their tracheae considerably increased ; the gemmule is seen 

 under the form of a cellular tumour without vessels ; the four 

 trachesR of the stem descend parallel to each other as far as the 

 radicular bulb, and thus constitute the medullary sheath ; no root- 

 lets are yet observable. A further stage of development exhibits the 

 same plant after the formation of rootlets, and the development of 

 one of the leaves of the gemmule. In this stage the cotyledons 

 have acquired a larger number of nervures ; the nervures of the 

 primordial leaf consist only of tracheae, two of which forming the 

 midrib descend by the stem to meet the four cotyledonary tracheae ; 

 in the stem or primary merithal (radicle of authors) these tracheae 

 are as yet solitary for two-thirds of the upper portion of their length, 

 but in the lower third they are accompanied and invested externally 

 by dotted ducts. At the limit between stem and root where the 

 rootlets are given off, the tracheae of the stem terminate, and we see 

 the commencement of the dotted or ligneous vessels, which begin to 

 ascend in bundles through the stem outside the tracheae and to de- 

 scend, unaccompanied by tracheae, through the roots and their rami- 

 fications. 



From his investigations Dr. Allemao infers, first, that the tracheae. 



