40 



that the cortex has entirely disappeared. The leaf gaps in such 

 a stem are conspicuous by their size. In the upper regions of 

 the stem in which the gap has not been buried in secondary wood, 

 they may measure from five to ten mm. in height and three to 

 five mm. in width at the base. 



The best material which the writer has seen is the decorti- 

 cated stems of Decodon venicillaiiis (L.) Elliott, an aquatic 

 perennial rather widely distributed in the eastern United States. 

 In this form, which is found on the borders of ponds, the aerial 

 stems die down every year, and commonly lie in the water all 

 winter. The action of the bacteria in the water in removing the 

 pith and cortex may be completed by boiling the stem a short 



Nodal anatomy in Decodon. bg, branch gap; bt. branch trace; Ig, leaf gap; 

 It, leaf trace. 



time in caustic potash. A face view of traces and gaps in this 

 form is seen in the accompanying figure. Although the gaps are 

 small, they may be easily studied with the naked eye. Except 

 toward the base of the slender stems, secondary growth is small 

 in amount, and the branch gap, which is commonly obscured 

 first by cambial activity, is readily distinguished. The leaf trace 

 is single, and the leaf gap extends upward until it merges with 

 the branch gap. The branch trace arises from the sides of this 

 common gap, and unites shortly after passing off from the stele. 

 The condition here illustrated is probably a common one in 

 woody plants. 



Dartmouth College 



