CHAPTER XVI. 



THE GROWING APEX 1 OF THE STEM DIFFERENTIATION OF 

 THE TISSUES COURSE OF THE VASCULAR BUNDLES. 



PRINCIPAL MATERIALS USED. 



Buds of Hippuris vulgaris ; fresh, or in alcohol; or Elodca canadensis ; or 

 Myriophyllum. 



Buds of Euonymus japonicus ; or of the Ash tree, Fraxinus excelsior; pre- 

 ferably in alcohol. 



Buds of Eqiiisetum arvense ; fresh, or in alcohol. 



PRINCIPAL REAGENTS USED. 



Eau-de-Javelle ; or concentrated potash and strong acetic acid Concen- 

 trated acetate of potash. 



IT will now be our task, by means of carefully-chosen examples, 

 to become acquainted with the structure of the growing apex of 

 plants, and the differentiation of the tissues which takes place 

 there ; and, incidentally, to learn something about the route of the 

 vascular bundles through the plant. 



Growing Apex of Hippuris. As the first example we choose a 

 Phanerogam, with a very strongly-developed and easily-prepared 

 "growing point," viz., Hippuris vulgaris (the Mare's-tail). We 

 take a strong shoot, cut off the end bud about ^ inch under the 

 apex, and first remove from it all the larger leaves. We then 

 hold the bud with the apex downwards, flat between the thumb 

 and index-finger, and endeavour to obtain a median longitudinal 

 section of it. For this purpose the razor is passed as perpen- 

 dicularly as possible between the two digits. First the bud is 



1 Variously known by the terms " growing point," " punctum vegctationis," 

 and " vegetative cone ". I adopt the term " growing apex " as at once correct, 

 and a suitable complement to the expression " apical growth," in so general 

 use. [Eo.] 



(204) 



