^?oCfl.A™S'] PKOCEEDINGS OF SOCIETIES. 217 



singular appearance, but the more probable exjilanation seems to be 

 that a layer of wood is deposited for every layer of bark, so that by 

 the time a new deposition of the bark is about to take place the wood 

 has already surrounded the extremity of the previous plate, in con- 

 seq[uence of which the progress of the new plate inward is barred by 

 the previous season's layer of wood. If this explanation be sound the 

 number of cortical plates on one side of, and including the primitive 

 cortical ray, indicates the age of the stem under examination. Each 

 annual layer of wood is thus broken up into four distinct portions by 

 the j)rojecting bark, each portion tilling up one of the sjiaces enclosed 

 by two of the arms of the cross. The number of plates formed on 

 each side of the foiu" primitive cortical rays rarely exceeds six. The 

 peculiarity of arrangement, to which I here draw attention, is so 

 striking, that it is a matter of surprise to see this featiu'e so badly 

 rci^resented in Gaudichaud's plates ; it is fairly drawn by Schleiden, 

 in his 'Principles of Botany,'* biit a better figure is given by Duchartre, 

 in his ' Elements de Botanique,' p. 167. 



Another arrangement of the cortical portion is also common. It 

 commences, as in the last method, with the projection of four slender 

 riiys into the midst of the woody fibres, reaching about half-way to 

 the pith ; but the next additions which take place are not found by 

 the side of the four primitive rays, as in the first-noticed arrangement, 

 but occur as four new projections placed exactly midway between the 

 first four, so that the stem now exhibits eight of these rays arranged 

 like the spokes of a cart-wheel. At first, the four secondary rays are 

 very much shorter in length than the four primitive rays, but as the 

 stem increases in age all the eight rays become of equal length. Even 

 in this type some species exhibit an approach to the first type, by some 

 of the primitive rays in the older stems having one or two lateral 

 plates lying alongside them. 



Perhaps the most striking form of all the Bignoniaceas which I 

 have hitherto examined is one which unites the peculiarities of both 

 the preceding arrangements, but carried to such an excess as that the 

 cortical portion at last forms one-half the bulk of the stem. Origin- 

 ally, the woody portion is arranged in the form of a cross, the bark 

 filling up the whole space enclosed by the four arms of the cross. 

 According as the stem increases in diameter, new cortical rays are 

 projected into the four extremities of the woody mass, so that the arms 

 appear to be bifid ; these bifurcations also in their turn become bifid, 

 and so the woody mass has its primary, secondary, tertiary, and qua- 

 ternary divisions according to its age. Further, as the innermost 

 cortical deposit — that surrounding the woody tissue — is very dark in 

 .colour, it throws into high relief the stellate outline of the woody 

 portion. I have met with only one or two sj)ecies of Bignonia which 

 furnish this elaborate arrangement, and the specimens exhibited will 

 show its striking character. 



The woody system of the stems belonging to this natural order is 

 by no means uniform, but it requires careful study before a detailed 

 description can be given. Nearly all the species, however, have 

 * Fp. 251, 252, uf the Eiigliah Iruus'.atiuii. 



