THE STEM 191 



type in higher dicotyledonous orders because the simple foliar 

 trace, which is a feature of the two groups under discussion, makes 

 the topographical conditions more easily understood. The Legu- 

 minosae in the case of the garden bean or, better, of the garden pea, 

 illustrate the situation appropriately for forms with plural traces. 

 At the same time the two types just mentioned, as well as the 

 tomato and the sage, exemplify the principle of recapitulation, 

 since, in all, the young stem is round and woody and only later 

 assumes the angular or furrowed configuration of maturity. The 

 hypocotyledonary region of the stem in the bean, for example, and 

 the lower region of the epicotyl in the pea both present a circular 

 and complete woody cylinder. The developmental evidence, as 

 also that derived from comparative anatomy, thus clearly points 

 to the derivation of herbaceous forms from woody ones and not 

 of arboreal perennials from annuals, logically following from the 

 account of the origin of the structures of the stem in dicotyledons 

 originated by Sanio and disseminated by Sachs and De Bary. 



Another feature of organization of herbaceous stems which often, 

 although not invariably, appears is the degeneracy of the rays other 

 than those broad masses of storage parenchyma which, as has been 

 set forth in the foregoing paragraphs, flank the foliar traces in 

 their vertical course in the stem. This situation is well illustrated 

 among the ranunculaceous representatives of the Ranales, for 

 example, the buttercup, the meadow rue, and the clematis. It 

 has already been discussed in sufficient detail in connection with 

 the vine type of stem in a former paragraph and therefore need not 

 be referred to here. 



The discussion of the herbaceous dicotyledons brings us to the 

 consideration of the stem in the monocotyledons. This important 

 group of plants, which in physiological efficiency excels all the other 

 large divisions of vascular plants, is practically entirely herbaceous 

 in its structure; and even in those of arboreal habit the internal 

 organization is that of herbs. The monocotyledons on account of 

 the relative simplicity of their fibrovascular strands have been 

 referred by many to affinities with the ferns or, on the basis of their 

 habit, to relationship with the older gymnosperms. These attri- 

 butions of relationship are, however, little supported by either 



