INTRODUCTION. 



23 



are continuous with the similar and synonymous tissues of the plerome of the stem 

 are formed, according to the data at hand, outside the plerome, being derived, as is 

 the whole leaf, from the periblem and dermatogen, or from the layers of meristem 

 corresponding in position to these. From all this we see then, that definite relations 

 between the original differentiation of the meristem and the formation and arrange- 

 ment of the definitive tissues obviously exist, but that these are not universally the 

 same. If then the course of treatment is to be uniformly arranged, we must for the 

 time being regard especially the distribution of tissues, while still keeping an eye 

 upon the differentiation of the meristem. 



In opposition to the foregoing view, another has lately been asserted, since Famintzin ^ 

 has undertaken to prove that in the Angiosperms definite systems of tissue, namely 

 besides the Epidermis especially the system of vascular bundles, are universally, i. e. in all 

 parts of the plant, each derived from the same primary layers of meristem, which are 

 separated even in the embryo, and develop further independently near and between one 

 another like the germinal layers of the animal body. The layers of meristem in question 

 are fundamentally the same above distinguished by us. On the share taken by the 

 dermatogen in the development of tissues there can be no two opinions; the main 

 question therefore is whether the system of vascular bundles arises universally, i. e. in 

 the whole plant from the same primary layer of meristem. If we ignore isolated cases 

 of controversy, the plerome or a certain region of it is in stem and root the initial part 

 for the system of vascular bundles, or for the greater part of them. The question there- 

 fore is whether the parts of the system of vascular bundles, which pass from the stem- 

 system into the leaves, and which belong to the latter, also arise from the plerome at the' 

 apex of the stem. This could not be otherwise effected than by outgrowths of the 

 plerome pushing between the other layers of the young forming leaf, and growing with 

 these, as was above asserted for the common growth of dermatogen and periblem, 

 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 periblem, since definite 

 bands of the latter show the corresponding 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 between the other tissues of 

 the leaf, and this proof he should have brought in order to establish his view ; he com- 

 municates rather observations, which lead to the contrary result. He asserts that the 

 leaf of the Papilionaceae mentioned, e.g. species of Trifolium, at a certain 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. 



' Botan. Zeitg. 1875, p. 501. — Beitr. zur. Keimhlatt-theorie im Pflanzenreich, Mem. Acad. St 

 Petersbourg, ? sdrie, torn. XXII. — Compare also Botan. Zeitg. 1876, p. 540. [Compare further 

 Pamintzin, Embryologische Studien, Mem. Acad. St. Petersbourg, torn. XXVI. No. 10, 1879.] 



' Compare especially Sanio, Botan. Zeitg. 1864, l.c^ 



