No. 508] STUDY OF VASCULAR ANATOMY 223 



gans, and sporangia ; and upon the layer-by-layer studies 

 of growing points. This means that an immense amount 

 of detailed work has been swept into the limbo for facts 

 at present useless. Early developmental studies of a 

 few forms seemed to establish definite sequences in cell- 

 divisions and definite functions for so-called generative 

 layers. This kind of research was its own corrective, for 

 as investigations multiplied, definite sequences and func- 

 tions disappeared in a maze of variation. The definite 

 thing proved to be not the details of development, but the 

 general organization developed. For example, the im- 

 portant facts in reference to the development of the 

 embryo are no longer thought to be the sequence of the 

 first dozen cell-divisions, but the organization of tissue 

 systems and organs. The leptosporangiate sporangium 

 may develop in a great many different ways, but the 

 general result is a sporangium of some definite type. 

 Particularly futile has proved to be the detailed study of 

 the development of independent gametophytes, for they 

 react remarkably to environment, and can be made to do 

 almost anything. At growing points it was once supposed 

 that each cell was predestined to contribute to one of the 

 generative layers, and dermatogen, periblem, and plerome 

 were traced through a mass of indifferent meristematic 

 tissue. After organization, they can be recognized; but 

 there is nothing definite in the details of their origin. 



It is generallv conceded that no great group of plants 

 has been derived from any other existing group For 

 example, the origin of pteridophytes from bryophytes is 

 liardlv a debatable question. The study of reproductive 

 structures alone made such a connection seem quite rea- 

 sonable to the scientific imagination. We had even 

 selected the responsible bryophyte forms, and snowed 

 how Anthoceros gave rise to the most primitive leafy 

 sporophvte. Now that much other testimony has accu- 

 mulated; such a connection is too difficult even for a vigor- 

 ous scientific imagination. Even the staunchest supporter 

 of this connection, and the one who has worked it out m 



