Mr. J. Miers on the Bignoniaceje. 265 



phyllous species are generically alike^ and they constitute a 

 group [Astathus) that may be regarded as a subgenus of Arra- 

 bidea. By this isolation, and with this exception, we maintain 

 a constancy in the rule of foliaceous development that I have 

 advocated. In the group just mentioned we meet with hetero- 

 morphous varieties, where, in consequence of some morpholo- 

 gical change in a few of their many 3-foliolate leaves, two 

 or all three leaflets grow together, assuming the state of a 

 single leaf, or of an unequal pair of conjugate leaves of an 

 unusual gibbous form : the mode of distribution of the nerves 

 in such cases shows that such coalescence is due to the same 

 kind of monstrous growth which, under similar exceptional 

 circumstances, we see in other families. As it sometimes hap- 

 pens that the cirrhus is wanting, it may be urged that one of 

 the folioles of a conjugate leaf may also be suppressed, and the 

 other reduced to the state of a simple leaf : of the possibility of 

 this occurrence there can be no doubt; but observation shows 

 that such instances are extremely rare, and then not universal 

 in the same plant, and must be held to be entirely of an excep- 

 tional character. Under the genus Panterpa, of which jB. leuco- 

 pogon, Cham., is the type, I have explained how, and under what 

 circumstances, simple and compound leaves occasionally occur in 

 the same plant ; but it is there shown that the simple leaves in 

 such cases partake of a stipuloid nature. These instances there- 

 fore cannot be said to affect the general rule above indicated. 



There is sometimes a peculiarity in the ligneous structure of 

 the Bignoniacea that merits attention : the stems of many of 

 them, in their transverse section, exhibit strong medullary rays, 

 not radiating from one common central point, as generally occurs, 

 but disposed in parallel decussating plates, in the form of a cross, 

 as shown by Plumier in Bignonia crucigera (PI. Am. Burm. tab. 78. 

 fig. A), and by Gaudichaud in Bignonia capreolata, B. unguis, 

 B. lactiflora, &c. (Rech. Org.Veg. tab. 14. fig. 4; tab. 18. figs. 4, 

 5, 6, 7, 8, 9 & 10) . The latter botanist remarks that this pecu- 

 liarity is more strongly developed in the plants of equatorial 

 regions : he adds that only four cruciform rays are at first seen ; 

 subsequently these are increased to eight, then to sixteen, thirty- 

 two, &c., and always in this geometrical pro- pig. OQ. 

 gression. I possess the stem of a Bignoni- 

 aceous climber from the region of the Organ 

 Mountains ; it is deprived of its bark, and is 

 about an inch in diameter : here four principal 

 rays are prominently developed, with four other 

 intermediate rays less strongly marked (fig. 20) ; 

 and corresponding with these rays, the stem has eight deep, 

 longitudinal, broadly gaping fissures, that run through its 



Ann. &^Mag. N. Hist. Ser. 3. Vol. vii. 18 



