-^ EXTRACTS AN'D ABSTRACTS. 377 



STEUCTtTEE OF THE GEOWING-POINT OF THE AnGIOSPERMOTTS E,00T. 



JJeler den vegetationspunht der Angiospermen- Wurzeln, insleson- 

 dere die Ilaulenlildung , von H. Gr. Holle. (" Botanische Zeitung," 

 April, 1876.) — The growing-point of most vascular plants shows, 

 besides sharp differentiation of Dermatogen, Periblem, and Plerom, 

 further segmentation of these into single rows and layers of cells, which 

 are constantly being formed, during the growth of the root-point, by 

 tangential division of the upper cells of the primitive Meristem. 

 Moreover, in all elevated groups of vascular plants the root-point, 

 owing to the different arrangements of single rows or masses of its 

 cells, presents different tijpes of structure. Naegeli and Leitgeb com- 

 pared the Angio-=permous root-point with that of Ferns and Horse- 

 tails, but their work is disfigured through the want to discover a 

 terminal cell in the former. The investigations of Hanstein and 

 Reinke resulted in the. establishment of a structure-type founded on 

 the root-point of Heliantlms, and these authors thought that this type 

 would be the general one for Monocotyledons as well as forDicotvledons. 

 In this, however, they were mistaken, for Strassburger found that 

 the Amentaceous root furnished an exception ; and Prantl discovered 

 an abnormal type in Pismn and Vicia, which Janczewski regarded as 

 forming a type of equal value to the Helianthus one, and, moreover, 

 showed that it is met with also in CucurUta. In the root-cap of the 

 last-mentioned genera we do not find ordinary Plerom, Periblem, and 

 Dermatogen, but a transverse primitive Meristem extends into the 

 middle of the root-cap, which it regenerates, and also builds up the 

 body of the root, the side portion of the cap consisting of Dermatogen, 

 as in the Helianthus type. With regard to Monocotyledons, an actual 

 Dermatogen was found by Janczewski only in Pistia and Hijdrocharis ; 

 in all other cases the Dermatogen is reduced to the single outermost 

 layer of the rind ; this, then, is one of the characters of the ordinary 

 monocotyledonous type, while Pistia and Hydrocharis have been 

 made into a special type by Janczewski. Finally, monocotyle- 

 donous roots are distinguished from dicotyledonous by the fact that in 

 the former the root-cap is formed from a special group of cells (Calyp- 

 trogen), while in the latter the Dermatogen takes on this function. 



On the subject of types the author holds an intermediate position 

 between Reinke and Janczewski ; he cannot agree with the former 

 that all Angiospermous roots come under one structural category, 

 neither does he consent to the establishment of several independent 

 categories. For Dicotyledons he admits a single very widely diffused 

 type — the Heliantlms type, to which all irregularities are to be 

 regarded as exceptions. 



The dicotyledonous root-cap consists of successively cast-off rows 

 of radially-arranged cells, each of the rows answering to a Dermatogen- 

 cell. In most cases these rows become unrecognisable in the further 

 part of the cap, through irregular development of the cells, but they 

 are often well seen in the roots of embryos, and sometimes — e.g., in 

 Rumex and Epilohium — in the mature plant. The neighbouring 

 Periblem differentiates, most generally, in the centripetal sense ; this 

 is not therefore an exceptional character, as Janczewski supposed. 



