INTRODUCTION. , . 343 



The classification here adopted does not therefore 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 habits 



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 2. 



Each of the four classes here proposed starts with very simple forms, and 

 attains, through diverging lines, very diff"erent 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 diff"erences 

 by comparing the most perfect forms of the diff"erent 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 Algte 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 characters sometimes points of great, 

 sometimes those of secondary morphological importance, as is shown by the names of the classes : — 

 Schizosporeoe, Zygosporese, Basidiosporeoe, Ascosporese, Tetrasporese, Zoosporese, and Oosporeoe 

 (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, 1 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 



