568 



MR. D. H. SCOTT OK THE ARTICULATED 



a very general rule in the development of these vessels, namely, 

 that the perforation of the lateral walls begins at an earlier stage 

 than thaLg)f the transverse walls *. 



The examination of the laticiferous tissue of the cotyledons 

 thus suffices to determine finally the true character of this tissue 

 in the species under consideration, and shows that here, as in 

 the genus Manihot, we have to do with articulated vessels, as di- 

 stinguished from the inarticulated cells of many other Euphor- 

 biaeea?. 



Fig. 1. Fig. 2. 



Fig. 1. Hevea brasiliensis. Port : on of tangential section from a vascular bundle 

 of a cotyledon at the commencement of germination. Part of a lati- 

 ciferous vessel is shown with a transverse wall broken down at one 

 side, at t. X360. 



Fig. 2. Similar preparation, showing transverse walls in process of absorption 

 at t, t l , and t 2 . At t the perforation is on one side ; at i! 1 and t 2 it is 

 central. X4C>0. 



The hypocotyledonary stem at the commencement of germi- 

 nation has a " thickening ring " in Sanio's sense ; that is to say, 

 between pith and cortex there is a zone of meristematic tissue 

 from which the vascular system is in process of development. It 

 is an interesting fact that whereas at this stage the xylem of 

 the bundles is but little developed, showing only a few elements 

 of the protoxylem with spiral thickening, the laticiferous tissue 

 is well advanced. It already forms an extensive network of 

 anastomosing tubes, lying on the outside of the thickening ring. 

 Here also traces of the absorbed transverse walls may be ob- 

 served. It is impossible to doubt that this tissue plays an im- 

 portant part in conveying the food-substances derived from the 



* Cf. Schmalhausen, Beitriige z. Kenntniss d. Milchsaftbehiilter d. Pflanzen, 

 1877, p. 23; Scott, Quarterly Journal of Micros. Sci. 1882, p. 148. Also the 

 p iper on Manihot above cited. 



