vi PREFACE 



some teachers this may seem to be an unnecessarily 

 large number of primary groups, especially to those who 

 have been in the habit of dividing plants into Thallo- 

 phytes, Bryophytes, Pteridophytes and Spermatophytes, 

 but we may remind all such that Engler in the seventh 

 edition of his "Syllabus der Pflanzenfamilien" divides 

 the thallophytic plants into eight primary groups, instead 

 of seven, as is done in this book. On the other hand the 

 Bryophytes, Pteridophytes, Calamites, and Lycopods 

 are brought into one primary division by Engler, and the 

 Cycads, Conifers and Flowering Plants into another. 

 We are assured that the phyla here recognized are natural 

 groups, and while they are by no means equally separated 

 from one another, they are easily distinguishable. This 

 is no less true for the phyla below the Bryophytes than 

 it is for those including and above this group. We 

 feel that the Calamites and Lycopods are entitled to 

 first rank independently of the Pteridophytes, and that 

 the latter and the Bryophytes are very certainly to be 

 treated as genetically separate phyla. In like manner 

 it seems to us that genetically the Cycads and Conifers 

 are so remote from the Flowering Plants that they can 

 no longer be placed in the same phylum, and that they 

 differ so much from one another that they must be 

 separated. 



Thirty-five years ago the treatment here given the 

 "lichens" would have called for explanation and defense; 

 now we are so familiar with their structure that the sug- 

 gestion that they were the first of the higher fungi will 

 cause little surprise. So, too, there is less need now than 

 formerly to defend the treatment of the Rust Fungi, 

 as to whose general relationship there is less and less dis- 

 agreement. With the growing acceptance of the struc- 

 tural homology of ascus and basidium in the higher 



