YampolskY: Siiuly of OU pal m. 125 



The line of demarkation between slieath and pétiole and base is very 

 sharp and it caii be seeii with the iiaked eye wheii youiig leaves are dis- 

 sected ont. Tliis is due to the criss cross arrangement of the fibres and 

 bundies of the sheatii in contrast with the adjacent parallel and vertical 

 arrangement of the fibres and bundies of the base and pétiole of the leaf 

 (Figure 12 Plate 11 and Figure 43 Plate VI). 



in examining a sheath in a young stage shown in Figure 44, Plate 

 Vi, we find that the tissue at the unattached end of the sheath is com- 

 posed of a layer of multicellular filaments in various stages of development. 

 The filaments however can readily be traced back to where they are ar- 

 ranged in parallel rows. The fact that thèse rows of cells end at différent 

 levels gives the scalloped form to the free end of the sheath. Figure 45, 

 Plate VI is a part of sheath taken from a stage shown in Figure 44 and 

 shows the arrangement of the layers in position YV. The free ends of 

 the parallel rows of cells terminate at différent levels. Figures 46 to 50 

 show the various stages of development of thèse hair like structures. 

 Figure 47 shows initial stages of growth of several of thèse hairs. The 

 plane of division is not constant ; it may be in a horizontal, vertical or 

 oblique plane. The hairs are both branched and unbranched. The 

 apical cell apparently is the one that is in active division. In the very early 

 stages the cytoplasm of the cells filling the whole lumen is vacuolated 

 containing tiny starch grains. The cells are colorless. As the hairs continue 

 to grow they elongate and take on the form shown in Figure 51 Plate VI. 

 In this stage the cytoplasm is seen bounding the periphery of the cells, 

 the starch grains hâve disappeared and the cells begin to degenerate 

 soon after. The above description refers primarily to the cells at the free 

 end of the sheath. 



On the inner surface of thèse sheaths and near the top may be 

 found minute stomata apparently fully formed, however without any 

 chlorophyll grains (Figure 52 Plate VI;. It is questionable whether thèse 

 ever function since they never reach direct light and therefore they must 

 be regarded as rudimentary. They are about one fourth the size of the 

 stomata of the leaf epidermis. 



With increased growth of the leaf as a whole, the sheath increases in 

 size; from the outer epidermis of the sheath as well as from the base of 

 the leaf and pétiole a dense felt like growth of hair arises, single or 

 branched, similar to the hair sliown in Figure 51 Plate VI. Between each 

 succeeding leaf until the outermost leaves are reached this dense felty 

 growth is présent and it is only when this felty growth reaches the out. 

 side that it dries up and falls off. In the meantime the bast strands of the 

 developing leaf become strengthened and more rigid so that when a stage 

 shown in Figure 43, Plate VI is reached, marked changes hâve occured. 

 The sheath has become tough and leathery and résistant to stress and 

 tsrain. The criss cross weave of the fibres makes a most résistant tissue. 



