200 The Anatomy of Plants 



with these. . . . Other investigators do not find this ; they 

 rather say that the vascular bundles in the leaf, like the 

 other inner parts of it, are derived from the primary peri- 

 blem, since definite bands of the latter show the corre- 

 sponding differentiation ; and that they are connected with 

 the system of the stem by reason of the relative position 

 of the said bands of periblem. Famintzin's researches 

 certainly afford valuable conclusions on certain processes, 

 but no new result on the main question. When he proves 

 that in foliage leaves, especially in the Papilionaceae, the 

 parts of the vascular bundle always arise from quite definite 

 layers of the meristem, he says nothing new ; for as the 

 mature vascular bundles in the leaf have a definite position 

 this must hold also for their younger stages. He does not 

 produce proof that these bundle-forming layers arise as 

 branches from the plerome layer in question of the stem, 

 and push themselves among the other tissues of the leaf, 

 and this proof he should have brought in order to establish 

 his view ; he communicates, rather, observations which lead 

 to the contrary result. He asserts that the leaf of the 

 Papilionaceae mentioned, e. g. species of Tri folium at a cer- 

 tain age, consists of five layers of meristem ; the outermost 

 is dermatogen or epidermis ; of the four inner, only the 

 two innermost are points of origin of the vascular bundles. 

 He further asserts that in an earlier stage, within the 

 dermatogen lies only one layer of meristem cells which, 

 according to our preceding statement, must be derived 

 from the periblem of the punctum vegetationis ; and that 

 the four later layers arise from division of the cells of that 

 one. It is clear that thereby the postulated pushing in is 

 excluded, and on this the theory of germinal layers must 

 be founded.' 



A somewhat different scheme of classifying the tissues 

 of the growing-point was proposed by Russow in 1872. 

 He recognized Sanio's thickening ring, which he called 

 Mesistem, and which he associated with the young cortex 

 termed by him Peristem, to form a layer of tissue sur- 

 rounding the young pith. He spoke of the latter as Endi- 

 stem, while he applied the term Existem to the mass of the 

 other two layers lying externally to it. This classification 



