November 11, 1904.] 



SCIENCE. 



621 



larity of structure often does not indicate 

 community of descent, and we are stag- 

 gered before the possibilities of phylogeny. 



The division of morphology that we have 

 been pleased to call cytology has had the 

 same experience. It was hoped that the 

 more fundamental structures would show 

 some reasonable constancy of phenomena, 

 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 dominated 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. 



3. THE PHASE OP THE INFLUENCE OP CHAN- 

 GING CONDITIONS UPON THE DEVEL- 

 OPING ORGAN. 



This means experimental morphology, 

 and so far as organs are concerned its pur- 

 pose is to discover the conditions that deter- 

 mine their structure and nature. All idea 

 of rigidity has disappeared in the funda- 

 mental conception of the capacity of living 

 cells to respond to varying conditions. 

 What may be the possibilities of variation, 

 and what may be the exact conditions re- 

 sponsible for variations, are questions to be 

 answered by experiment. If the oldest 

 morphology is in its decline, and the cur- 

 rent morphology at its culmination, exper- 



imental morphology may be said to be in its 

 inception. It is easier to judge of a move- 

 ment at its decline or culmination than at 

 its inception, and experimental morphology 

 as yet is fuller of promise than of perform- 

 ance. In any event, it was an inevitable 

 phase when multiplied variation had 

 broken down the conception of rigidity. 

 The fundamental question of the possibili- 

 ties of living cells is immediately confront- 

 ing 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 

 illustration. 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 condi- 

 tions rather than of the narrow x'ange of 

 possible response on the part of the organ. 

 From this point of view an organ is rep- 

 resented by its essentials, without reference 

 to its non-essentials, and so we are now 

 thinking of sporangia in terms of sporogen- 

 ous tissue, without reference to the pres- 

 ence or absence of a morphologically con- 

 stant wall; of arehegonia as axial rows of 

 potential eggs, without concern for an ex- 

 act morphological definition of the sterile 

 jacket. The main question is, what de- 

 termines the formation of sporogenous tis- 

 sue rather than of sporangia; what deter- 

 mines the formation of eggs or sperms, 

 rather than of arehegonia and of an- 

 theridia ? 



2. The Possibilities of Pnmordia..— This 

 has to do with what I have called the doc- 

 trine of predestination. It is more than 

 a question as to the variable form or struc- 

 ture of an organ; it is a question as to 



