INTR OD UC TION. 24 £ 



off. In the genus Vaucheria we find all stages of transition from motile cells to 

 gonidia which simply fall off. • 



The Classification of Thallophytes has been till quite recently based essentially 

 on characteristics relating merely to the mode of Hfe, according to which they have 

 been divided into three classes, — Algae, Fungi, and Lichens; the Characese have 

 been sometimes included under Algae, sometimes altogether separated from Thallo- 

 phytes. But since more accurate investigations have enabled us not only to elucidate 

 the morphological significance of the growth of these plants, but also to discover the 

 sexual organs in the main divisions, and in many cases to follow the whole course of 

 development, this classification can no longer be maintained, since it depends 

 essentially only on differences in the external appearance and mode of life, while on 

 the other hand it is seen that a totally different classification is necessitated by their 

 morphological characteristics. The admirable labours of Schwendener, for example, 

 have shown that Lichens, hitherto considered as a separate class, must not only be 

 included among Fungi, but must be regarded as a section of a particular order, the 

 Ascomycetes. Since we have become more accurately acquainted with the sexual 

 organs of the Coleochoeteae and FlorideoD, it can scarcely be doubted that these Algae 

 have a close affinity to Characeae in the structure of their fructification. We can 

 therefore now distinguish only two classes of Thallophytes, — Algae and Fungi. But 

 it has long been admitted that it is impossible to draw any satisfactory boundary-line 

 between these two classes ; several writers have indeed frequently pointed out that 

 some families of Fungi must be closely associated with certain families of Algae. It has 

 been recognised more and more clearly that these .two classes are separated only 

 by a single distinguishing character; if the two old-established groups are to be 

 retained, the only distinction between the two (and the one adopted in the earlier 

 editions of this book) is to place under the head of Algae all those Thallophytes 

 which contain chlorophyll, under the head of Fungi all those which do not. But 

 this separation is altogether artificial, and could only be tolerated so long as want of 

 an accurate knowledge of the morphology of these plants compelled us to admit 

 a classification having no foundation in morphology. In the present state of our 

 knowledge, in which at least the morphological foundation for a scientific classi- 

 fication of Algae and Fungi may be laid down, it is not only permissible but 

 incumbent, in the interest of progress, at least to attempt a morphological classi- 

 fication of Thallophytes. 



The first point to note is that the presence or absence of chlorophyll can be 

 no sufficient reason for separating plants which are nearly related to one another 

 morphologically, and which agree in their structure, their sexual organs, and their 

 alternation of generations. In Phanerogams this principle is thoroughly admitted. 

 If all Flowering-plants which do not contain chlorophyll were formed into one 

 class in contradistinction to those which do contain it, the Rafflesiaceae, Balanopho- 

 raceae, Corallorhiza, Cuscuta, Orobanche^ Monotropa^ &c. would have, in spite of 

 the differences in their organic structure, to be combined into one class, and 

 removed from their true relationship. No one however disputes that Cuscuta 

 belongs to the Convolvulaceae, Orobanche- to the Labiatiflorae, Monotropa to the 

 Pyrolaceae, and Corallorhiza to the Orchideae. These affinities are inferred, among 

 Phanerogams, chiefly from the structure of the flowers and the embryo, and no one 



