W. Bateson 95 



T A B LE — continued. 



Type Sport 



4. Epidermal cells: upper Small: tcith both upper li&Tgev.nothickeniiifjofloioer 



and lower cell-ioalls cell-ioalls 



thickened 



5. ditto lower No clear difference 



6. Palisade cells Elongated in vertical Shorter, wider, less crowded 



plane : compressed to- and less compressed : more 



gether, and regular in irregular in shape 

 shape 



7. Layers of palisade cells Variable. 1 — 3 layers Less variable : mostly one 



layer, occasionally more 

 than one 



8. Spongy parenchyma... No clear difference 



9. Bases of hairs ... Raised More raised than in type 



When shiny and dull areas exist in the same leaf all stages of tran- 

 sition from the typical form to the other occur very irregularly. The 

 change from thick cuticle to thin cuticle can be fairly abrupt, but the 

 change in the shape of the palisade cells is more gradual and very 

 irregular. A few "sport" palisade cells can occur in areas of "type" tissue 

 and vice versa, and the differences are not so clearly defined in the in- 

 ternal tissues as might be expected from the external appearance of 

 the leaf The fixation of the transitional parts is difficult, and no good 

 microtome preparations have so far been obtained. The two types of 

 tissues react differently with the same fixative; the "sport" tissue is 

 penetrated more rapidly than the "type" tissue, and hence is fixed sooner 

 than the "type." 



The shiny appearance of the short leaf is possibly due to : 



(1) Thickness of cuticle. 



(2) Flat surface of the epidermis. 



(3) Fewer hairs which are more erect and somewhat finer as com- 

 pared with the bent hairs of the sport. 



The darker green appearance of the same leaves is probably due to: 



(1) Longer, more densely packed palisade cells. 



(2) Extra layers of palisade which occur somewhat irregularly. 



D. M. Cayley. 



The inclusion of cells belonging to either form within the tissues of 

 the other is especially remarkable. 



