THE STELE 7 



there is a layer, or a series of layers, of cells which undergo 

 division both in planes pprpendicular to and in planes parallel to 

 the surface of the stem. These are known as the perihlem. On 

 tracing them backwards down the shoot we find them continuous 

 with tissues which immediately beneath the epidermis are com- 



, ,^^^- 2.— -Growmg-point of stem, showing apical meristein. P, plerome ; B, peri- 

 blem ; E, dermatogen ; J, rudiment of leaf. (After Leunis and Prank.) j 



monly green, and which often have their cells much thickened 

 in the corners in herbaceous plants or shoots, whilst still further 

 back, on older parts of woody shoots, the'^green layer is often 

 buried under one or more layers of brown ~ cork. These tissues 



Pig. 3.— Terminal bud, showing growintf-point of stem, overlapped by rudimentary 

 leaves with buds m their axils, the whole covered by dermatogen. In the centre is 

 the stele to which descend the midribs of the leives. (After Prantl.) 



which thus originate in the periblem are known collectively as the 

 cortex. 



It is with tissues originating from the central plerome or stele 

 that we are mainly concerned. If we cut a young shoot across, a 

 little below its entirely embryonic apex, we shall see that, whilst 



