98 THE ORIGIN OF MONOCOTYLEDONS [CHAP. 



can become hereditary by appearing when the 

 plant is raised from seed and grown on land, as 

 in the figwort. But when a plant is amphibious, 

 growing on land or in water, the power of 

 adaptation to either is retained, but appears 

 not to be hereditary. Thus (fig. 23) shows a 

 section of a root of Bidens cernua in water 

 and on land. In the latter no lacunae or air- 

 chambers are present ; but in the water-plant 

 there are large ones both in the cortex and path. 

 Moreover, other indications of degeneration are 

 seen, as in the much reduced mechanical tissues 

 or woody bundles, etc. 



With regard to rhizomes and aerial stems, 

 the former in the water-lilies is precisely like 

 monocotyledonous stems. The origin of the 

 irregular arrangement of the woody strands may 

 be traced to some extent in Nelumbium? the 

 Lotus, because, in that plant, the fibre-vascular 

 bundles are still arranged in a long internode in 

 concentric circles. The rive outer zones are 

 traceable into leaves. If we compare this with 

 such simple herbaceous flowering-stems as those 

 of anemone and narcissus, which have their 

 strands in more than one zone, we begin to see 

 that the zones in Nelumbium represent a first 

 stage in the degradation of the compact xylem- 

 cylinder characteristic of woody dicotyledons. 



This last condition is the result of response to 



1 " Comp. Anat. of Phan. and Ferns/' by De Bary, p. 255, fig. 112. 



