b2 COMPENDIUM OF GENERAL BOTANY. 



even at a very short distance from the primary meristem of the 

 apex. The typical dicotyledonous bundle possesses cambium dur- 

 ing its entire life-period. The elements of the vascular bundles 

 of the monocotyledons also had their origin from cambium, but 

 the formative tissue soon becomes changed into permanent tissue- 

 elements, and in regard to the individual bundle this change pro- 

 ceeded centripetally ; the sieve-tube tissue (leptome) and the ves- 

 sel-bearing portion (hadrome) with the accompanying mechanical 

 cells lie in close proximity. In dicotyledons and conifers the cor- 

 responding tissues namely, the secondary cortex, which is formed 

 outwardly by the cambium, and the wood, formed inwardly are 

 always separated by the cambium. In winter there is at least one 

 cell-layer of the cambium, which represents the separating boundary 

 between the cortex and wood. The cortex, which is formed from 

 the first or primary meristem of the stem-apex, and which there- 

 fore existed before the appearance of the cambium-ring, is called 

 primary cortex, in distinction to the cortex formed by the cambium. 

 It does not show the characteristic radial structure seen in the sec- 

 ondary cortex. 



The customary way of speaking of the monocotyledonous bun- 

 dles as ' ' closed ' ' and those of dicotyledons as 4 ' open ' ' is rather 

 unfortunate, 1 for the monocotyledonous bundles are opened toward 

 the fundamental tissue by means of special structural arrangements 

 (transit-cells, large thin- walled cells, etc.), while the dicotyledo- 

 nous bundles form a closed complex by means of the cambium, so 

 that the individual bundle is scarcely recognizable as such. There- 

 fore the fundamental tissue of dicotyledons and conifers is plainly 

 divided into cortex and parenchyma (medulla), a peripheral and a 

 central portion, which have an anatomical-physiological connec- 

 tion through the medullary rays. In monocotyledons the boundary- 

 line between cortex and medulla is also often well marked, at least 

 in the numerous cases in which the bast-ring represents the me- 

 chanical system. From some statements made by SCHWENDENER 

 on p. 71 of his ' ' Mechanische Princip " it would seem that 

 such demarcation between the cortex and the medulla of mono- 

 cotyledons without a bast- ring is not easily demonstrated. With 

 regard to the radially diagonal course of many leaf -bundles in mon- 



designated the monocotyledonous bundles not as "closed," but as 

 " enclosed," which is more nearly correct. 



