140 MORPHOLOGICAL DEVELOPMENT. 



Lentinus flab elli for mis, of which e and e' are different views, 

 exhibits complete bilateralness — a bilateralness in which 

 there is the greatest likeness of the parts that are most simi- 

 larly conditioned, 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 further class of facts which are the con- 

 verse 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 

 Thallophytes, as in the tubers of underground fungi and in 

 the creeping films of sessile lichens, which severally show us 

 variations of proportions obviously caused by variations in 

 the amounts of the influences on their different sides, we also, 

 among Archegoniates 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-organized aggregate of the second order, not individuated 

 by the mutual dependence of its parts, has its form deter- 

 mined by the balance of facilities and resistances which each 

 side of the frond meets with as it spreads. 



§ 219. Among plants displaying 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, have 

 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 

 marked unlikeness between the two parts of their environ- 

 ment, soil and air; are facts too conspicuous to be named 



