THE GENERAL SHAPES OF PLANTS. 125 



shown in elevation at d and in section at d. And A. flaheUi' 

 formis, of which, e and e are different views, exhibits com- 

 plete bilateralness — a bilateralness in which there is the 

 greatest likeness of the parts that are most similarly condi- 

 tioned, and the greatest unlikeness of the parts that are most 

 dissimilarly conditioned. 



Among plants of the second order of composition, it will 

 suffice to note one farther class of facts which are the con- 

 \^erse of the foregoing and have the same implications. These 

 are the facts showing that along with habitual irregularity in 

 the relations to external forces, there is habitual irregularity 

 in the mode of growth. Besides finding such facts among 

 Thallogens, as in the tubers of underground fungi and in the 

 creeping films of sessile lichens, "which severally show ua 

 variations of proportions ob\dously caused by variations in the 

 amounts of the influences on their different sides, we also 

 among Acrogens of inferior types, find irregularities of form 

 along with irregularities in environing actions. The fronds 

 of the Marchantiacece or such Jungermanniacece as are shown in 

 Figs. 41, 42, 43, illustrate the way in which each lowly-or- 

 ganized aggregate of the second order, not individuated by 

 the mutual dependence of its parts, has its form determined 

 by the balance of facilities and resistances which each portion 

 of the frond meets with as it spreads. 



§ 219. Among plants that display integration of the third 

 degree, and among plants still further compounded, these 

 same truths are equally manifest. In the forms of such 

 plants we see primary contrasts and secondary contrasts, 

 which, no less clearly than the foregoing, are related to 

 contrasts of conditions. 



That flowering plants from the daisy up to the oak, havo 

 in common the fundamental unlikeness between the upward 

 growing part and the downward growing part ; and that 

 this most marked unlikeness corresponds with the most mark- 

 ed unlikeness between the two parts of their environment, 



