THE STEM 



189 



rays on page 82, that the herbaceous stem may result from the 

 breaking up of the originally continuous woody cylinder through 

 the formation of special storage devices in connection with traces 

 of the leaves. This process is far more striking in the more delicate 

 annual stems by reason of the slender character of the cylinder. 

 It is apparent that the conditions found in the stem of the oak, etc., 



FIG. 141. Diagram of stem of Labiatae. Explanation in the text 



as regards the presence of large foliar rays, elucidate the origin of 

 th e herbaceous type. 



The situation illustrated in Fig. 140 is not, however, by any 

 means a universal expression of the topography in herbaceous stems. 

 It will be well to show further possibilities in this direction by 

 reference to a family of dicotyledons much higher in the scale than 

 are the Rosaceae. In Fig. 141^ is shown the perennial stem of 

 the common garden sage, Salvia officinalis. The outside is covered 

 with an armor of periderm within which lies the narrow cortex, 



