INTERCELLULAR SECRETORY RESERVOIRS. 



453 



The branches obsen^ed by Trecul in Rhus viminah's, which pass into the wood, pass 

 off nearly at right angles from the cortical bundles, and into the medullary rays, without 

 reaching the medullary passages. 



The vascular bundles passing into the petiole, which are arranged in curves in its 

 transverse section, and branch in their further course, take with them one passage each 

 from the stem : these passages have the same position as those in the primary bundles. 

 The same is the case with the stronger branches of the bundles, while the passage is often 

 absent in the weaker ones. In addition to these passages there are in the petiole of Rhus 

 semialata medullary passages also, which lie 1-3 together on the inside of the strongest 

 bundles ; in the petiole of Spondias cytherea one is placed opposite the inner margin of 

 the median bundle. A similar arrangement, the details of which may be read in Trecul's 

 work, is found in the mid-ribs of leaves and leaflets ; these contain several vascular 

 bundles, which turn their phloem, and also the resin -passages sometimes towards the 

 upper, sometimes towards the lower surface of the leaf. All lateral ribs contain but one 

 passage turned towards the lower surface of the leaf, and even this is absent from the 

 last branches of the bundles. In Rh. semialata and glauca Trecul saw the passages of 

 the leaf-lamina anastomosing in a reticulate manner like the vascular bundles, which 

 they accompany. 



According to van Tieghem's investigations of Bursera gummifera, and the transverse 

 sections of branches of species of Balsamodendron and Protium figured by INIarchand ^, 

 there is found in these balsam-bearing trees of the order Burseracex a structure of the 

 cortex similar throughout to that described in the Anacardiaceae, and the same distribu- 

 tion of the gum-resin passages in the roots, the stems and their branches, and the 

 petioles. 



In the genera A'llantus and Brucea ', now placed among the SimariibecE, there are 

 longitudinally-running sap-passages, as in many species of Rhus, at the periphery of the 

 pith of the stem ; in Ailantus glandulosa as many as 60 ; in other regions of the stem they 

 are wanting. They appear, according to accounts at hand, to traverse the successive 

 internodes, and to give off branches at the nodes into the leaves; this is not, however, dis- 

 tinctly stated. At all events the passages are again found in the petioles and the mid-rib 

 of the leaflets, and in the pith-like parenchyma surrounded by vascular bundles arranged 

 in curves or rings, or lying between these. They are not present in the lateral ribs 

 which are given off from the mid-ribs of the leaflets. 



* L. Marchand, Recherches pour servira Thistoire des Burseracees ; in Baillon, Adansonia, torn. 

 VII. p. 258, pi. Vni, et torn. VIII, pp. 17, 74, pi. II., III. 



* Trecul, Vaisseaux propres des Terebinth acees, I.e. 



