No. 508] STUDY OF VASCULAR ANATOMY 227 



This fact of " lagging behind" is coming more and 

 more into evidence. I do not mean by this that the 

 lagging structures always advance sooner or later, for 

 they may simply persist as veterans. A conspicuous 

 illustration of it is found in the evolution of the micro- 

 sporangiate and megasporangiate structures of seed- 

 plants. In the most primitive group of seed-plants 

 known, the Cycadofilicales, the microsporangia are still 

 at the fern level, produced in the same relations and of the 

 same general structure as are the sporangia of ferns; 

 while the megasporangiate structure has become a highly 

 organized ovule, which in some way has replaced the 

 sorus. The relations to the sporophyll are the same, but 

 the structure has become very much changed. There is 

 an enormous hiatus in our knowledge in reference to the 

 heterosporous ancestors of these primitive seed-plants, 

 but during all that development of heterospory to the 

 seed-condition, the microsporangia remained practically 

 stationary. Even among the Mesozoic Bennettitales, the 

 microsporangia are still fern-like synangia, although a 

 highly organized strobilus has been developed ; and among 

 modern cycads the same persistent lagging of the micro- 

 sporangia is evident. All this means that no single char- 

 acter, however primitive, can establish the phylogenetic 

 level of a group. All the testimony must be in, and 

 especially the history, before one can feel any reasonable 

 assurance as to conclusions. 



The new conception of the monocotyledons is so clearly 

 a triumph of vascular anatomy that the other phase of 

 morphology is hardly entitled to a share in it And yet, 

 now that it is evident that the monocotyledons are a 

 specialized offshoot from the primitive dicotyledonous 

 stock, many things in the older morphology become 

 clearer. There are those intergrades, as they may be 

 called, between the monocotyledonous and dicotyledonous 

 condition, which have given so much trouble to the pigeon- 

 hole botanist, who insists that a given seed-plant must be 

 a monocotyledon or a dicotyledon. We recognize now 



