SUNFLOWER APICAL BUD 83 



Note on passing back from the apex towards the 

 more differentiated part of the stem a gradual increase 

 in length of the cells, corresponding to the gradual 

 extension -of the internodes, while in the first elon- 

 gated internode of the stem below the bud this is very 

 marked. Observe also the various stages of the pro- 

 cess of vacuolization of the protoplasm ; this will be 

 best seen in sections stained with hsematoxylin, and 

 mounted in Canada balsam (see p. 52). 



Apical buds of the Jerusalem Artichoke (HeliantJius 

 tuberosus) may be used instead of H. annuus, and they 

 have the advantage of being purely vegetative buds. 

 Whereas the Sunflower flowers early, the Artichoke 

 does not flower at all in this country : thus the 

 complications which attend the formation of flowers 

 will be avoided. 



Buds of the Common Lilac (Syrmga vulgaris) afford good 

 material for the study of the apex of the stem : the winter buds 

 may be used either fresh, or hardened in alcohol. The great 

 advantage of this bud is that the leaves are of regular decussate 

 arrangement, and thus by cutting in the median plane of one of 

 the outer pairs of leaves, successive inner pairs will also be 

 traversed in the median plane when the bud is exactly halved. 

 As in the Sunflower, median longitudinal sections are to be cut : 

 treat them for a time (varying with the thickness of the sections) 

 with "eau de javelle"; wash with water, and then with weak 

 acetic acid : mount in glycerine. 



In such preparations the apex of the axis will be found to be 

 almost flat, and covered by the continuous dermatogen : the 

 leaves originate from the superficial tissues at its margin, the 

 greatest activity of cell-division being in the hypodermal layer. 

 (Compare Fig. 6.) 



In cases where the apical cone is broad, as in Helianthus, the 

 tissues, with the exception of the dermatogen, are usually not 



G 2 



