MODIFICATIONS OF FORM 



203 



these successive stages out into detail, though they are found to 

 follow certain definite methods. The point is that from a cyclic 

 beginning a spiral disposition is arrived at. As the individual plant 

 develops and its apex expands, the complexity of the arrangement 

 of its appendages increases. The individual life of the Sunflower 

 illustrates a relation that is usual, viz. that complex spiral arrangements 



Fig. 136. 



Transverse sections through the apical buds of branches of Araucaria excelsa of different sizes. 

 (After Church.) The uppermost is of a branch of the first degree (7+11): the lower, left, a 

 branch of the second degree (5+8) : the lower, right, one of the third degree (3+5). 



are found where a widened axis develops with short internodes, and 

 where the crowded primordia of leaves are of relatively small size. 

 Such spirals occur either in the vegetative or the floral region. Very 

 beautiful examples are seen in the vegetative shoots of Araucaria 

 excelsa of various size (Fig. 136). A biological consequence is that 

 with verv numerous leaves each obtains a maximum exposure to 

 light incident from above. Moreover, since the branching is axillary 

 in the flowering plants, the position of the branches themselves will 



