Jan. 1900.] BOTANICAL SOCIETY OF EDINBURGH 349 



colours all lignified and corky elements, while the former 

 is exclusively absorbed by protoplasmic and cellulosic 

 structures.^ 



The Phellogenetic Divisions. — The initial divisions of the 

 phellogen, which in this species arises in the cells of the 

 epidermis, are purely centripetal in direction, and, under 

 normal conditions, the few centrifugal divisions which 

 ultimately occur do not take place till a later period. 



The origin of the rootlet, however, considerably precedes 

 the first appearance of phellogen, and the relative rate of 

 growth of these two structures is, in general, such that by 

 the time the root has penetrated to within two or three 

 cells of the outer limit of the primary cortex the phellogen 

 has undergone from one to three centripetal divisions, with 

 the result that the outer persistent portion of the original 

 epidermis is separated from the dividing layer by one or 

 two rows of cork cells. 



This relation between the rates of growth of these two 

 almost independent tissues, though fairly constant, is 

 subject, as might be expected, to certain variations. It 

 may, for example, happen that for some reason the origin 

 of the root is somewhat delayed or its growth retarded in 

 comparison with that of the phellogeu, as indeed appears 

 to occur normally in the case of the last formed roots of a 

 year's growth. 



On the other hand, the elongation of the root rudiment 

 may altogether outstrip the formation of phellogeu, a con- 

 dition which may be readily brought about artificially by 

 placing in water a shoot of the current year, after removal 

 of as much of its basal portion as exhibits well-marked 

 papillffi. When so treated the young root rudiments already 

 formed in the stem increase so rapidly in length as to force 

 their way to the exterior, perforating both cortex and 

 epidermis before even a trace of phellogenetic division has 

 appeared in the latter. 



Every stage intermediate between these two extremes 



1 The sections are soaked in a saturated aqueous solution of 

 Malachite-green till deeply stained, and then treated directly with a 

 saturated alcoholic solution of Magdala-red, washed rapidly in absolute 

 alcohol followed by origanum oil and mounted in balsam, — a method of 

 obtaining a double stain for which I am indebted to my friend Dr. 

 Campbell Brown. 



