282 



METAMORPHOSIS 



one or more adjacent anticlinal cell rows which by their active growth create 

 a prominent swelling on the outer surface of the growing point. The cells of 

 the periclinal row, 7F, take scarcely any part in the formation of this swelling, 

 while on the other hand, pericline /// shows extreme activity both in growth 

 and in cell formation, and the swelling so formed is covered by the periclinal 

 layers // and /. Layer // has become double, but the outermost layer (/) 

 remains, as elsewhere, unilamellar. The leaf rudiment grows progressively 

 along with the growing point of the stem from which it arose ; later on, 



Fig. 80. Median longitudinal section of the root apex of Horde 'um vulgare. , initial cells of the root-cap ; 

 r, cells of the cap about to be thrown off; pi. central-cylinder; en, endodermis ; /', intercellular spaces; 

 </, epidermis ; c, thickened external wall of the epidermis. From STRASBURGER (Das botanische Prakticnm, 4th 

 ed., Jena, 1902). 



when growth becomes more marked perpendicularly to the plane of the 

 drawing, the flattened dorsiventral shape of the typical leaf is assumed. 

 The lateral buds arise in the same way as the primary growing point of the leaf. 

 The manner in which the young leaf is attached to the growing point of the 

 stem is worthy of notice. At first the leaf rudiment has approximately the 

 form of a hemisphere, whose surface in contact with the stem is nearly 

 circular in outline (elliptical or rhomboidal). Frequently, however, this pro- 

 jection proceeds to grow in two directions, encircling the growing point, so 

 that finally it forms a ring-like wall, whose greatest height lies medianly or oppo- 



