MORPHOLOGY OF ANGIOSPERMS. 121 



leaf, as in the acacias, of Australia; or it may become bladder- 

 like and serve as a means for floating the plant, as in the water 

 hyacinth. The stipules may likewise be modified, becoming leaf- 

 like, as in the pansy (Fig. 70) ; or metamorphosed into thorns, as 

 in the locust; or clasping, as in Polygonum. In some cases the 

 leaves are very much reduced, their functions being performed by 

 the stem, as in Cactaceas, or even by the roots, as in some orchids 

 which have assimilating roots. 



Prefoliation or vernation is the disposition of leaves in the 

 bud. The terms used to describe the folding of the leaves in the 

 bud are derived from an examination of transverse sections of 

 the bud. The following are some of the terms which are em- 

 ployed : coNDUPLiCATE, when the lamina of the leaf is folded 

 lengthwise along the midrib so that the two halves of the upper 

 surface lie together, as in the Magnoliacea;; plicate or plaited, 

 when the lamina is folded along the veins, like a closed fan, as in 

 the maples ; convolute, when rolled lengthwise and forming a 

 coil in cross section, as in the Rosacece; involute, when both mar- 

 gins are inrolled lengthwise on the upper surface, as in the violets ; 

 REVOLUTE, when both margins are inrolled lengthwise on the lower 

 surface, as in Azalea. 



In addition, there are several terms used which are derived 

 from the appearance of the bud, as reclinate or inflexed, when 

 the upper part is bent on the lower, as in Liriodendron ; and 

 circinate, when the upper part is coiled on the lower so that the 

 tip of the leaf is in the center of the coil, as in the ferns. 



IV. THE FLOWER. 



Structure of the Flower. — It is well known that if a por- 

 tion of the stem of a plant, including one or more nodes, be placed 

 under suitable conditions for growth, roots will arise from the 

 nodes that are in the ground and a new plant will be developed. 

 This method of increasing the number of individuals is frequently 

 resorted to by horticulturists, and is known as vegetative propa- 

 gation. The process is wholly asexual and depends upon the 

 division of old cells to form new ones. It is fortunate, however, 

 that owing to the special conditions required in this method of 



