842 



A TEXTBOOK OF THEORETICAL BOTANY 



The axillary buds, upon which branching depends, arise from the super- 

 ficial tissues of the main growing point, and are thus exogenous. The bud 

 rudiment arises immediately above a leaf rudiment and exactly on the same 

 radius (Fig. 835). That is to say, that buds are invariably median in the 



axil of the subtending leaf. Except in the 

 flowering shoots of some plants the ap- 

 pearance of a bud rudiment always follows 

 the appearance of a leaf rudiment, and 

 extra-axillary buds are never formed at the 

 apex. Some variation, however, exists in 

 the relationship of the bud and the leaf. 

 The bud may sometimes appear on the 

 surface of the axis, or in other cases it 

 may be formed from the actual base of the 

 leaf. No special morphological signific- 

 ance need be attached to such variation in 

 itself, but it has interesting morphological 

 consequences. Later growth may inter- 

 vene to separate the bud considerably from 

 its point of origin. When the bud stands 

 on the stem it may thus be carried up- 

 wards on the internode, indeed the whole 

 elongation of the internode sometimes 

 occurs between the bud and its leaf axil, 

 so that the bud seems to lie just below the 

 node above. From this circumstance arise 

 the numerous cases of the so-called adhesion 

 of branches to their parent axis or of branches 

 or flowers arising from points other than 

 the axil of a leaf. All such cases can be 

 traced to the displacement of axillary buds. 

 When, however, the bud stands on the leaf base the subsequent growth 

 of the latter may lead to the appearance of shoots or flowers arising from a 

 point on the surface of the leaf, a circumstance extremely puzzling to older 

 morphologists, who regarded the leaf as an organ fundamentally different 

 from the shoot. 



The opposite case may also occur when the bud, or the zone of tissue on 

 which it stands, elongates before the leaf has fully developed. Then the leaf 

 appears to be attached to the axillary branch which it actually subtends. 



All these peculiarities arise from the phenomenon of intercalary growth, 

 that is, growth in length which occurs in any part of a plant away from the 

 growing point itself and therefore not part of the main growth system which 

 centres there. 



In general, it may be said that whichever organ of the pair, leaf and 

 axillary bud, originates first will develop first. Normally this is the leaf, and 

 in many cases the appearance of the bud rudiment in its axil may be delayed 



Fig. 835. — Acer pseudoplatanus. 

 Winter buds. 



