218 PROCEEDINGS OF SOCIETIES. [*Jo!lmLl AprU M«a^ 



numerous vessels of large diameter imbedclecl in the woody tissue, 

 so that the stems are for the most j)art very light and porous. Such 

 an arrangement might have been expected in plants whose stems are 

 only as thick as a linger, and whose sap has to travel a long distance 

 before it can reach the leaves, which are for the most part met with 

 only in the uppermost j)ortions of the stems. In most of the species, 

 this woody tissue is traversed by a large number of fine medullary 

 rays, which give a beautiful figure to many of the sections. Their 

 internal arrangement does not manifest itself in any marked way on 

 theii' exterior ; their form is generally cylindrical, but some of them 

 exhibit four- slight projections in the form of narrow raised bands 

 arranged lengthwise, which corresj)ond with the outermost portions of 

 the four cortical rays. Some species have a square stem during their 

 early growth, and even the older stems do not altogether lose their 

 four-sided character. 



The constancy of the figure four as the radical number is very 

 noticeable in the structure of the different parts of these stems, and 

 there can be little doubt that it originates in the decussate arrange- 

 ment of the leaves. The stems of the Mints, Sages, and many other 

 British plants furnish us with ready examples of a quadruple arrange- 

 ment of parts. 



Malpigldacece. — If the lianas which belong to the Bignoniacese are 

 remarkable for the symmetry of their parts, the lianas of this family 

 may be said to be characterized by an absence of symmetry. In 

 general, their stems are singularly rugged in outline, a section pre- 

 senting deep sinuosities or ii-regular projections, while at other times 

 they appear to be made uj) of a number of separate branches which 

 have become consolidated in the progress of growth, so as to form a 

 rough-looking roj)e of many strands. 



Jussieu gives a full and interesting accoimt of the structure of one 

 of these stems, the Sticjmaplujllon emarginatiim* and Gaudichaudf figures 

 an allied sjiecies ; but I have not, as yet, identified either amongst those 

 coming with cotton. I exhibit, however, a stem which appears to be 

 the Tetrajpterys Guilleminiana referred to by Jussieu, and figured by him 

 in his Monograph ; J but this species does not exhibit the sinuosities 

 so characteristic of most of the lianas of this family. 



As a general rule, the woody matter is developed unequally round 

 the central i)ith in the form of irregular lobes, the bark closely follow- 

 ing all the sinuosities of the stem. If the lobes increase on one side 

 of the stem only, the pith soon becomes eccentric ; but, on the other 

 hand, in many sjjecies, while the pith retains its central position, the 

 irregular growth of the woody lobes — each of which is closely invested 

 by the bark — causes some to grow beyond their neighbours, and these 

 latter, in the progress of growth, become imbedded, with their bark, 

 in the midst of the woody matter j)roduced by the more vigorous lobes. 

 A stem in tliis adult state therefore presents the greatest irregularity 

 of form, particularly in the genera Banisteria and Heteropterys. 



Sapindacece. — In this natiu'al order we meet with some wonderful 



* Me'moire,' &c., pp. 103, &c. 



t ' Kecherches,' &c., pi. xviii., fig. 11, p. 129. 



X Plate ill., fig. 5, p. lOG. 



