PRACTICAL BOTANY 



which ascend from the lower. The cortex stops short 

 below the apex of the leaf, which is accordingly termin- 

 ated by a series of naked cells. 



3. Follow the leaves down to their base of insertion 

 at the node, and observe a series of short cells which 

 project more or less below the point of insertion : these 

 are the so-called " stipules." The axillary bud will also 

 be seen inserted in the axil of the oldest leaf of the 

 whorl. 



A comparison should be made of the structure of some species 

 of Nitella, and its simpler construction noted, involving no cortex 

 either on stem or leaves. The single large internodal cell should 

 be examined, and it will be seen to present a smooth wall, enclos- 

 ing a colourless protoplasm, in the peripheral part of which 

 are numerous green chlorophyll grains : these are so disposed 

 that a spiral line may be seen running longitudinally, in 

 which they are entirely absent : this is the neutral line as regards 

 the protoplasmic movements. 



III. Remove and examine a -whole bud under a low 

 power : either an apical or an axillary bud will do. It 

 may be necessary to treat with acetic acid to remove the 

 lime, which is often present in considerable quantity : 

 the bud may be subsequently cleared with potash, and 

 mounted in glycerine. The outer and older leaves will 

 show the characters above noted, but more clearly, 

 since they are younger, and their internodes shorter : 

 the structure of the cortex will thus be better under- 

 stood in the young than in the mature leaves. 



Examine also the cortex covering the short, young 

 internodes of the stem, and recognize the regular arrange- 

 ment of the cells : the cortex of each internode is 

 composed of two series of lobes, the one ascending from 

 the lower node, the other descending from the upper : 



