126 MORPHOLOGICAL DEVELOPMENT. 



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

 not important items in tlie argument. More instructive, 

 perhaps, because less familiar, is the fact that we miss this 

 extreme contrast in flowering plants which have not their 

 higher and lower portions exposed to conditions so extremely 

 contrasted. A parasite like the Dodder, growing in entan- 

 gled masses upon other plants, from which it sucks the juices, 

 is not thus divisible into two strongly-distinguished halves. 

 Leaving out of consideration the difierence between the 

 supporting part and the supported part in phasnogams, and 

 looking at the supported part only, we observe between its 

 form and the habitual iacidence of forces, a relation like that 

 which we observed in the simpler plants. Phaenogams that 

 are practically if not literally uniaxial, and those which de- 

 velop their lateral axes only in the shape of axillary flowers, 

 when uninterfered with ordinarily send up vertical axes round 

 which the leaves and flowers are disposed with a more or less 

 decided radial symmetry. Gardens and fields supply us 

 with such instances as the Tulip and the • Orchis ; and on a 

 larger scale the Palms and the Aloes are fertile in examples. 

 The exceptions, too, are instructive. Besides the individual 

 divergences that arise from special interferences, there are 

 to be traced general divergences where the habits of the 

 plants expose them to general interferences in anything 

 approaching to constant ways. Plants which, like the Fox- 

 glove, have spikes of flowers that are borne on flexible foot- 

 stalks, have their flowers habitually bent round to one face of 

 the stem : an unlikeness of distribution probably caused by 

 unlikeness in the relation to the sun's rays. The wild Hya- 

 cinth, too, with stem so flexible that its upper part droops, 

 shows us how a consequent difierence in the action of gravity 

 on the flowers, causes them to deviate from their tjrpically 

 radial arrangement towards a bilateral arrangement. 



Much more conspicuous are the segeneral and special re- 

 lations of form to general and special actions in the environ- 

 ment, among phsenogams that are multiaxial. That when 



