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 
