46 The Nature and Origin of Stipules. 



stamens, and the corona of Silene ma}^ ver}^ probabl}' represent a 

 ligule. The glands of the leaves of Ranunculaceie which have 

 been homologized with stipules, as already stated, can often be 

 traced up into the flowers and are familiar in connection with the 

 petals of Ranunculus. 



One of the most interesting families of plants in the develop- 

 ment of its stipules is that of the Rubiaceae, the development 

 being ver^- unusual in the group of the Stellatse. Though the 

 foliar anomaly in this group was early remarked upon and was 

 anatomicall}' explained as early as 1840,* there are considerations 

 which make its present discussion desirable. 



In the greater part of the family the leaves are opposite, or oc- 

 casionally in whorls of three as in Cephalanthus occidentalis L., 

 and are usually- stipulate. The stipules are of variable character 

 and often Interpetiolar, the adjoining stipules on each side of the 

 stem being connate. In the group of the Stellatae however, com- 

 prising ten or twelve genera, the stipules usuall}'^ are apparently 

 wanting and the leaves in whorls. There is a tendenc}' toward a 

 verticillate arrangement of the leaves in others of the Rubiacete, 

 as shown by the frequent occurrence of whorls of three in usually 

 opposite-leaved species. Now an anatomical examination of the 

 whorled leaves of Mollugo verticillata L., Silene stellata (L.) 

 Ait. f., Lej)tandra Virginica (L-) Nutt. and Cephalanthus occi- 

 dentalis L. reveals the fact that in other families, as well as in 

 the Rubiaceae exclusive of the Stellatffi, each leaf of any whorl 

 receives its fibro-vascular bundles directly from the cauline cjdin- 

 der. But in Galium the case is different. Two leaves only of 

 the whorl receive their bundles in the manner stated, and only 

 these two produce buds in their axils. All the others receive their 

 vascular supply from what may be termed a nodal girdle, each 

 half of which is formed by the union of two bundles arising, 

 one from each of the two leaf-traces in the same manner as those 

 supplying stipules of the ordinary form. From this girdle arise 

 the bundles which supply the additional leaves, whether there be 

 only one on each side, as in Galium circsezans Michx. and G. 

 lanceolatum Torr., two, as in G. triflorum Michx. and G. tinc- 

 torium L., or even three or four, as occurs in G. Aparine L. The 

 distribution of the vascular bundles may be seen in a cross sec- 

 tion of the node of Galium tinctorium L. (fig. 77). 



* See page 6. 



