204 Maine Agricultural Experiment Station. 1920. 



epidermis which at this point assume an irregular and peculiar 

 shape (Fig. 34, lower part). They appear here short and broad, 

 and have a more transverse orientation, which is of importance 

 in connection with the breaking through of the coleorhiza. Fol- 

 lowing these cells is a layer of strongly thickened, silicious, 

 mainly hexagonal cells. They lie parallel to each other and are, 

 about the middle of the base, arranged in longitudinal series 

 while at either side of the base they form transverse, fan-like 

 layers. These cells terminate with a ring of quite short, round- 

 ish-polygonal cells which form the outermost lower border of 

 the base of the lemma. With this ring of short cells the lemma 

 rests upon the rachilla. The rachilla appears as a columnar pillar 

 whose elements are composed of elongated cells. The epidermal 

 cells are very thick, appear round on cross-section, and some of 

 them run out into hairs. The epidermis is followed by 2 to 3 

 layers of thick-walled, pitted, sclerenchymatous cells while the 

 parenchymtous tissue fills out the central part of the rachilla, 

 and surrounds the fibrovascular bundles. Towards the base of 

 the lemma the rachilla broadens somewhat and its long cells 

 terminate with a ring of quite short round cells which border 

 directly on the ring of similarly developed cells forming the 

 lowermost layer of the base of the lemma. At maturity these 

 two rings separate and the fruit thus becomes detached from 

 the rachilla. 



No less striking is the differentiation of the mechanical 

 elements of the prosenchymatous tissue. As will be seen from 

 Fig- 35 A. a. C. this tissue is composed above the basal region of 

 the lemma of elongated, interlocking, pointed sclerenchymatous 

 cells. At the base," however, they lose their sclerenchymatous 

 aspect, their longitudinal diameter decreases, their lumen in- 

 creases, their pointed ends are transformed into oblique or al- 

 most horizontal septae until they assume an entirely different 

 aspect at the base of the lemma, as illustrated in Fig. 35 B. 



This differentiation in form is accompanied by a reduction 

 in the number of presenchymatous cell-layers in the region where 

 the coleorhiza breaks through. While above the base the pro- 

 senchyma is composed of 5-7 layers, it is reduced at the base to 

 but one layer. The reduction of the epidermis is also caused by 

 the disappearance of silicious cells and the decrease in the thick- 

 ness of the cell walls. However, along the outer edge of the 



