LECT. VI.] THE STEM. FIGURE. 273 



able Hydrangea, Hydrangea hortemis, may be 

 taken as examples of the round ; but the term is 

 more or less applicable to all stems which ap- 

 proach to the circular form and have no angles. 



b. Half round (semiteres), (fig. s, 2), that is, 

 round on one side and flattish on the other. 



c. Compressed (compressus), (fig. s, 3), which 

 implies that two sides of the stem are flat, and 

 approach each other, or that the diameter of a 

 transverse section of it is much greater one way 

 than it is the other ; as in flat-stalked Meadow 

 Grass, Poa compressa. Besides the compressed 

 stem, properly so called, there are two other 

 forms of stems, which may be regarded as va- 

 rieties of it : a. the two-edged (anceps), (fig. s, 

 4), when a compressed stem has the edges 

 sharp, like a two-edged sword ; as in striated 

 Sisyrinchium, Sisyrinchium striatum ; and @. 

 the leaf-like membranaceous (phylloideus mem- 

 branaceus), when the stem is so much flat- 

 tened as to resemble a leaf; as in Spleenwort 

 Cactus, Cactus phyllanthus. 



d. Angled (angulatus), which means that 

 a stem presents several acute angles in its cir- 

 cumference. There are three principal varieties 

 of angled stems. 



a. Obtuse (obtuse angulatus), when the 

 angles are rounded and the sides flat. There 

 are five sub-varieties of the obtusely angled 

 VOL. i. T 



