INTRODUCTION. 
The classification here adopted does not theretbre make any pretension to 
be one which will endure for all time ; it rather claims to be in accordance with 
the present state of our knowledge, and to bring into proximity those forms which 
agree in the most important features of their development. In a certain sense 
this classification may still be called an artificial one ; but it is natural in so far as 
it attempts to bring into prominence actual affinities and not merely differences and 
resemblances of external habit \ 
It is, as every one knows, easier to make objections to a system than to lay 
down clear principles on which one should be established ; and we will therefore 
only add a few explanatory remarks respecting the following table. In the present 
state of our knowledge, we seem compelled, first of all, to establish a class of 
Thallophytes in which not only is sexual reproduction unknown, but in which 
there is no near affinity to any sexual forms ; this class will include only the 
simplest and most minute of all plants, and is therefore formed into the first 
class under the name Protophytes. But in a large number of Thallophytes in 
which we are unacquainted with the sexual organs, there is an obvious close affinity 
with well-known forms, with which therefore they may be associated in classification. 
Finally, there are other Thallophytes in which the sexual organs are still unknown, 
but in which no distinct affinity is exhibited with the Protophytes or with other 
well-known forms. These plants are altogether omitted from our classification, 
since it is not my purpose to present an index of all existing forms, but only to 
show the affinities of those that are best known ^. 
Each of the four classes here proposed starts with very simple forms, and 
attains, through diverging lines, very different degrees of development. The closest 
affinities are therefore found by comparing the simplest primary members of each 
class, especially those of the 2nd, 3rd, and 4th classes ; and the widest differences 
by comparing the most perfect forms of the different classes. In this respect 
therefore these proposed classes resemble the recognised divisions in the groups 
of Muscinese, Vascular Cryptogams, and Phanerogams. 
In order not to depart too widely from the classification still current, and 
to facilitate a general view, I shall, as will be seen from the following table, treat 
separately the forms which contain chlorophyll (so-called Algae) from those destitute 
of chlorophyll (so-called Fungi) within each class ^ 
^ Cohn, who was the first to give up the division of Thallophytes into Algj3e and Fungi, has 
not been, in my opinion, so happy in the classes which he has proposed. He does not start 
from any definite principle, but employs as his typical chai-acters sometimes points of great, 
sometimes those of secondary morphological importance, as is shown by the names of the classes : — 
Schizosporese, Zygosporese, Basidiosporeee, Ascosporeae, Tetrasporese, Zoosporese, and Oosporece 
(see Hedwigia, 1872, p. 18). 
2 [Reference for some criticism and additional details on this classification of the Thallophytes 
may be made to Quart, Journ. Micr. Sc. 1875, pp. 295-326, and pp. 396-401 : see also de Bary, Bot. 
Zeitg. 1881. For a Classification of Fungi, see de Bary, Beitr. IV. 1881.] 
"^"-^ Since this classification and the following account of Thallophytes has been ready for the 
press, I have had the opportunity of seeing a letter addressed to Dr. Brefeld by Prof. Fischer 
(Oct. 29th, 1873), in which the following classification is proposed: — 
THALLOPHYTES. 
Myxomycetes. Fungi. Algae. 
R 2 
