146 WAKE-ROBIN. 



LABORATORY WORK. 

 GROSS STRUCTURE. 



I. GENERAL CHARACTERS. Observe: 



1. The main axis consisting of a thickened, horizontal under- 

 ground stem, the rhizome or root-stalk, and a single verti- 

 cal branch, the aerial stem, bearing a terminal flower. 



2. The root-stalk, bearing as lateral appendages the roots 

 and modified leaves in the form of broad membranous 

 scales. 



3. The aerial stem, bearing as lateral appendages a whorl of 

 three foliage leaves, and the parts of the flower, in five 

 whorls. 



II. THE ROOTS. Observe: 



1. Their arrangement on the root-stalk. 



2. The absence of branching. 



3. The surface, especially the transverse wrinkles on older 

 parts. What is the significance of the wrinkles ? 



If quite fresh specimens are used, it may be possible to see: 



4. The root-hairs. 



III. THE ROOT-STALK (RHIZOME). Observe: 



1. Its shape and thickness. 



2. The succession of nodes and internodes. 



a. Their number in an unbroken root-stalk. 



b. The scars of former branches, and the varying number 

 of intervening nodes. 



c. The irregular growth of the internodes. 



3. The apical bud and its protecting scales. 



4. Sketch a piece of the root-stalk with some of the roots 

 growing upon it. 



IV. THE BRANCH (aerial stem). 



1. The absence of nodes below the whorl of leaves. 



2. The smoothness of the surface. 



