126 



MORPHOLOGY OF TISSUES. 



latter, on its part, sometimes runs out beneath the apex into a single cell (in 

 Hippuris and Udora ca?iadejisis, according to Sanio), but usually terminates in a 

 somewhat subordinate group of cells. 



While in Cryptogams with an apical cell, an evident cell of this kind is first of 

 all formed where a lateral outgrowth (shoot, leaf, root) is about to be newly formed 



on the pufichim vegetationis, in Pha- 

 nerogams, on the other hand, a whole 

 group of cells, including inner and 

 outer layers, becomes developed at 

 the spot in question, so that even at 

 the first commencement of an organ, 

 no one predominating apical cell can 

 be recognised (Fig. 103,/'^'). After 

 Sanio ^ had investigated these pro- 

 cesses in Phanerogams, Hanstein^ 

 studied them in a more general and 

 detailed manner, and has recently 

 shown especially that even in the em- 

 bryo of Phanerogams the first divi- 

 sions take place in such a manner 

 as to exclude from the first the ex- 

 istence of an apical cell ; on the 

 other hand, a differentiation into an outer layer and an inner nucleus of tissue 

 soon manifests itself^. 



The outermost layer of the primary meristem which covers the punctum vege- 

 laliofiis together with its apex is the immediate continuation of the epidermis of the 

 older part which lies further backwards ; it may therefore be termed the Primordial 

 Epidermis ; Hanstein has however already applied to it the name Dermatogen. 

 It is distinguished by the circumstance that divisions occur in it exclusively at right 

 angles to the surface (it is only at a subsequent period that tangential divisions also 

 sometimes occur when the epidermis consists of several layers). 



Beneath the Primordial Epidermis are generally found one or more layers which 

 also cover the apex continuously, and out of which the cortex originates further back- 

 w^ards from the apex (Fig. 112, rr, p. 141) ; they represent therefore the Primordial 

 Cortex ; Hanstein calls this layer of the primary meristem the Periblem. Enclosed 

 and overarched by this is a nucleus of tissue, which may be followed out as an imme- 

 diate continuation of the fibro-vascular bundles, and of the pith enclosed by them, as 

 is shown in Fig. 112, where the later woody tissue {//), together with its vessels 

 igg) and the pith (w), run out into a group of primary meristem, w^hich, lying be- 

 hind the apex {s), is covered by the primary epidermis and the primary cortex. The 

 thickening-ring of Sanio mentioned in an earlier paragraph, in which the first fibro- 



FiG. 103. — Longitudinal section through the apical region of the stem 

 of an embryo oi Phaseolus miiltijloriis ; ss apex ; /5 part of the two 

 first leaves ; k k their axillary buds. 



^ Sanio, in Bot. Zeitg. pp. 184 et seq. 1865. 



^ J. Hanstein, Die Scheitelzellgruppe im Vegetationspunkt der Phanerogamen. Bonn 1868. 

 ^ J. Hanstein, Monatsber. der niederrh. Gesell. July 5, 1869. For further details see the general 

 characteristics of Phanerogams in Book II. 



