DEVELOPMENT OF MORPHOLOGICAL CONCEPTIONS 7 



phytes; and the beautifully distinct sporangium of the leptosporan- 

 giates compelled the idea of an imbedded sporangium among the 

 eusporangiates. In other words, the concept included non-essential 

 with essential structures, a distinct wall about a sporangium being 

 just as much a part of the definition as the sporogenous tissue, and its 

 presence compelled even in the absence of any occasion for it. It can 

 hardly be doubted that this was a heritage of habit from the older 

 morphology, for .it is in a sense a continuation of the conception of 

 types. The recent morphologist who traces a sporangium wall into an 

 anther is the same in spirit as the older morphologist who saw in the 

 stamen a transformed leaf. 



Associated with this rigidity of conception as to structure was the 

 idea of predestination, and search was made for the cell or cell-group 

 that was foreordained to produce a given structure. There was no 

 idea that the fate of these cells might be changed or that other cells 

 might share it. The repeated attempts to discover an exact definition 

 of the term archesporium will serve as an illustration; and the re- 

 peated failures should have warned sooner than they did. Indif- 

 ference of primordia was not thought of, and each living cell was 

 conceived of as having only a single possibility. 



The idea of unvarying sequence and predestination not only en- 

 tered into the conception of developing organs, but also directed an 

 immense amount of work in connection with the early embryonic 

 stages of both gametophyte and sporophyte. So far as my own experi- 

 ence is concerned, it was in this connection that the conception of 

 rigidity broke down. The multiplication of observations caused defi- 

 nite sequence and predestination to vanish in a maze of variations. 

 This type of morphology was necessarily its own corrective, for rigid- 

 ity could not stand before the accumulation of facts. In a sense, rigid- 

 ity of conception is easier to grasp, and certainly simpler to present, 

 than flexibility of conception, for the human mind seems to demand 

 its knowledge in labeled pigeon-holes. This same spirit permeated 

 the attitude of the morphologist of this period towards his ultimate 

 purpose, for phylogeny to him was rather a simple conception. Sim- 

 ilarity of structure meant community of descent. Such a condition as 

 heterospory, such a structure as the seed, or such an organization as 

 the sporophyte, was attained once for all, and the successful plant or 

 group became the fortunate ancestor of all heterosporous plants, or 

 spermatophytes, or sporophytes. This was phylogeny made easy. 

 Multiplied observations showed that similarity of structure often does 

 not indicate community of descent, and we are staggered before the 

 possibilities of phylogeny. 



The division of morphology that we have been pleased to call cyto- 

 logy has had the same experience. It was hoped that the more funda- 

 mental structures would show some reasonable constancy of phe- 



