8 BIOLOGY 



nomena r some rigidity in detail; but we have been confronted here 

 again by endless variation, and hence most diverse interpretation of 

 results. 



Clearly, belief in a rigid sequence or in predestination could not be 

 maintained; and in a real sense morphologists have been cataloguing 

 material for study, and their real problems lie behind these endlessly 

 variable details. 



The phase of morphology just described has certainly been domi- 

 nant during the last half-century, with phylogeny as its chief 

 stimulus, and a rigidity of conception that only a multitude of facts 

 could break down. It is a type that must always exist, as taxonomy 

 must always exist, and it must be considered fundamental in 

 familiarizing with material; but, perhaps, it may be said now to be 

 at its culmination as the dominant phase. 



III. The Phase of the Influence of Changing Conditions upon the 

 Developing Organ 



This means experimental morphology, and so far as organs are 

 concerned its purpose is to discover the conditions that determine 

 their structure and nature. All idea of rigidity has disappeared in 

 the fundamental conception of the capacity of living cells to respond 

 to varying conditions. What may be the possibilities of variations 

 and what may be the exact conditions responsible for variations, 

 are questions to be answered by experiment. If the oldest morpho- 

 logy is in its decline, and the current morphology at its culmination, 

 experimental morphology may be said to be in its inception. It is 

 easier to judge of a movement at its decline or culmination than at 

 its inception, and experimental morphology as yet is fuller of pro- 

 mise than of performance. In any event, it was an inevitable phase 

 when multiplied variation had broken down the conception of rigid- 

 ity. The fundamental question of the possibilities of living cells is im- 

 mediately confronting us; and the range of these possibilities may 

 be considered under three heads. 



(1) The Varying Structure of an Organ. Perhaps leaf variation, 

 which enters so largely into taxonomy, may be used as an illustra- 

 tion. When, under experimentation, leaves can be made to vary 

 from narrow to orbicular, from dissected to entire, and the exact 

 physical condition determined that induces the result, any idea of 

 rigidity in the form or structure of an organ must disappear. An 

 observed narrow range of variation in nature may be regarded as an 

 indication of the narrow range of conditions rather than of the nar- 

 row range of possible response on the part of the organ. From this 

 point of view an organ is represented by its essentials, without refer- 

 ence to its non-essentials, and so we are now thinking of sporangia in 



