PROBLEMS OF PLANT MORPHOLOGY 87 



est the common point of derivation. It seeks, then, with diligence 

 after "primitive" forms. But in this search we meet with great 

 difficulties. In the first place, we are inclined to regard those 

 forms as primitive which have simple form-relations, and unmarked 

 division of labor. But such forms may also have arisen by reversion, 

 and if one looks over botanical literature, he sees, at least so far as 

 the relationships between the larger groups are concerned, there ex- 

 ists no agreement as to which forms are to be regarded as primi- 

 tive and which derived; opinion on this point often changes with 

 the fashion. Thus the thallose liverworts have up till now been 

 regarded as more primitive than the foliose, because the vegeta- 

 tive body of the former is much more simple in construction than 

 that of the latter, and between them there are found gentle grada- 

 tions. Recently, however, the attempt has been made to derive 

 the thallose from the foliose forms. 1 This is not the place to exam- 

 ine the evidence for or against such derivation. How vacillating is 

 the point of view from which it is judged what form is primitive is 

 shown by the various positions which have from time to time been 

 given to the apetalous dicotyledons. 



The old morphology regarded these as reduced forms because their 

 flowers are less fully differentiated than those of most of the other 

 dicotyledons. Eichler has, however, already shown that there is no 

 ground for maintaining that the corolla in the luliflorce and 

 Centrospermce has suffered reduction; and on this point we can 

 only agree with him. But must they, because the perianth shows 

 simply form-relations and also because the number-relations within 

 the flower are not always constant, be therefore primitive? Even if 

 we admit that these groups have a great geological age, it is not 

 proved that they stand as regards their total organization on a 

 lower plane of development; old and primitive forms are the same 

 only when it can be shown that the former stand nearer to the 

 stem forms of the angiosperms than other forms. If this is not 

 capable of proof, then the old forms may just as well be the end 

 terms of long developmental series as others, only that the differentia- 

 tion of organs has not taken place to the same degree as in the others. 

 Now, we do not know the stem forms of the angiosperms, and they 

 may never, perhaps, be known. But even if we content ourselves 

 by reconstructing them on the basis of comparative study, I can 

 find no reason, e. g., to regard the Cupuliferce as primitive forms, 

 while I can find many reasons for not doing so. Here may be cited 



1 Wettstein, Handbuch der Systematischen Botanik, n, p. 26, 42. It is certainly 

 suggestive to regard the development of organs from various points of view. I can- 

 not, however, regard the attempt of Wettstein as wholly well-founded. It is quite 

 true that among the liverworts, a thallus may arise at times from a leafy stem. I 

 have shown this for Pteropsiella (Cephalozia) frondiformis Spr. (Goebel, Rudimen- 

 tare Lebcrmoose, Flora, 1893, p. 84). But the grounds for regarding this true in 

 general for the thallose liverworts appear to me not to be at hand. 



