THE GROWING POINT 



277 



the floral regions of the higher plants, and transitions may be obtained between 

 such forms and the depressed growing point, where somewhat older parts grow 

 round the real ' apex ' so as to form a kind of crater, while the younger organs 

 develop progressively downwards on its inner wall (Fig. 71). It may be noted in 

 this relation that this form of growing point may occur not only owing to de- 

 pression during its development from the rudiment up to its definitely completed 

 state (e.g. many flowers), but that the depression maybe induced by supplemen- 



Fig. 71. Longitudinal section through 

 the capitulum of a sunflower. The central, 

 somewhat depressed, growing point shows 

 as yet no rudiments of flowers. Slightly 

 enlarged. 



Fig. 7i. Longitudinal section of the bud of 

 ;i Phanerogam, i/, growing point ; y, leaf rudi- 

 ments; g; axillary bud(x lo). From the Bonn 

 Textbook. 



tary modifications. In the latter case, the depressed situation of the growing 

 point protects this very delicate part from possible injuries from the environ- 

 ment. Such protective arrangements are attained, however, in other ways. In 

 the formation of huds, for example, the lateral members grow more rapidly than 

 the apex of the growing point, curving over in such a way as to enclose 

 it. Fig. 72 will give an idea of the appearance of such a bud in longi- 

 tudinal section. In other ways also, e. g. by inrolling 

 of lateral members, a protective arrangement is not 

 infrequently acquired by dorsiventral growing points 



(Fig. 73). 



We know now that the duty of the growing point 

 is, while continually elongating its own axis, to give 

 rise also to lateral axes. The same relations in general 

 obtain on these lateral branches as on the chief axis. 

 They have each at least one growing point, originally a 

 process from the chief growing point ; it elongates into 

 an axis of secondary rank and eventually gives rise in 

 turn to lateral axes. The lateral branches of the first 

 order, however, do not all behave alike, and even in many Algae one can 

 distinguish two types : those which behave in all respects like the main axis, 

 long shoots, and those whose growing point after a short time loses its activity, 

 the short shoots. The distinction is not, however, of much importance and 

 intermediate conditions are not infrequent. 



There are quite special relationships in the highest plants, and especially 

 among the Phanerogams, which demand our attention. The shoot bears on 

 its axial region, the stem, special lateral appendages which we term leaves- 



Fig. 73. Herposiphonia rt- 

 pens. V, growmg point. After 



GOEBEL(l88o). 



