GERMINATION 



937 



Within the bud scales are delicate embryonic leaves that are most eco- 

 nomically arranged as to utilization of space, a particular kind of 

 arrangement, known as vernation, often being characteristic of special 

 plant groups. 



Leaves in the bud may be plane ; conduplicate, or folded inward, as in the bean; 

 plicate, or folded in pleats, as in the beech; crumpled, as in the poppy; involute, 

 or with the halves rolled inward, as in the violet; revolute, or with the halves rolled 

 outward, as in the dock; convolute, or with the leaf rolled from one margin to the 

 other, as in the canna; or circinate, that is, with the leaf rolled inward on itself from 

 the apex downwards, as in ferns (fig. 382). It is believed that the kind of verna- 

 tion is due in part at least to the limitations of space within the bud ; by experi- 

 mentally restricting this space, the leaves of Prunus which usually are flat become 

 crumpled, and by cutting the stipules, the leaves of Magnolia become flat. 



External factors in relation to bud germination. The germination of 

 winter buds is associated largely with spring, and, as with seeds, it takes 

 place when the temperature becomes sufficiently high to permit water 

 to enter the embryonic shoot in abundance and to incite it to activity. 

 Buds differ from seeds in being em- 

 bryonic shoots rather than embryonic 

 plants, and usually also in remaining 

 attached to the plants that bear them 

 (except in the winter buds of water 

 plants), the water used in germina- 

 tion thus coming from the plant rather 

 than from the ground. As shown 

 elsewhere, buds often appear to be 

 mature before they are capable of ger- 

 mination, the maturation process seem- 

 ing to consist in part in the accumula- 

 tion of food. Germination may be 

 hastened by placing a plant or even 

 a branch indoors in winter. Only local 

 stimuli are needed for germination, as 

 is shown by growing a single branch 

 detached from a plant and placed in 

 water indoors, or by training a branch 

 from a tree into an adjoining house, 

 or even by supplying favorable temperatures locally to a part of a 

 plant outside, as by bending a willow branch, into a sheltered position; 



1232 



1233 



FIGS. 1232, 1233. Bulblings of 

 Cicuta bulbifera; the first bladeless 

 leaves or phyllodes (p) are followed 

 by foliage leaves (/) ; b, bulbil. 



