324 The Botanical Gazette. [December, 



the simplest of living forms, and it seems more probable that 

 of living Algae, the higher Confervaceae such as Coleochcete, 

 come nearer to this hypothetical form. 



The first of the groups with which we have to deal, the Bryo- 

 phyta, or Muscineae, is readily divisible into two classes, the 

 liverworts (Hepaticae), and true mosses (Musci). There has 

 been some controversy as to which of these is nearest the 

 primitive stock, and to the higher plants. A comparison of 

 the two groups will show, however, very strong reasons for 

 considering the Hepaticae as the more primitive group. Al- 

 though far outnumbered in species by the true mosses, the 

 Hepaticae show a much greater diversity of form, both of the 

 gametophyte and sporophyte than is the case with the Musci, 

 which form a remarkably close group with relatively insignifi- 

 cant differences (excepting in the case of Sphagnum)', and 

 the higher ones, with their very peculiar and highly special- 

 ized sporogonium, are evidently very remote from any other 

 group of plants. The Hepaticee, on the other hand, offer a 

 very strong contrast to this. Several divergent stocks are 

 evident, all traceable to a common form and touching in cer- 



tain respects, Algae, M 



The thallus 



of such simply organized forms as Anthoceros or P cilia, is but 

 a slight advance on the higher green Algae, although it must 

 be borne in mind that this simplicity does not extend to the 

 ual organs and sporophyte. On the other hand, these 

 same forms are connected directly with the Musci through 

 Sphagnum, and as the writer has endeavored to show be- 

 fore, * to such pteridophytes as OpJiioglossum. 



If we now study a little more closely the relation of the 

 Hepaticae, inter se\ we can distinguish three well-marked 

 series of forms diverging from a common stock. Nearly all 

 liverworts pass through a more or less well-marked thallose 

 stage which is persistent in some of the simpler thallose 

 Jungermanniaceae such as Aneura and Metzgeria. This is a 

 simple flat often heart-shaped thallus, growing from a single 

 apical .cell. It is usually, although not always, traversed by 

 a well-marked mid-rib. The frequent recurrence of this stage 

 in the development of so many forms of Hepaticae, as well as 

 tn the prothallium of the isosporous ferns, is most readily ex- 

 plained by the assumption that this represents the ancestral 

 type from which both groups have sprung. Granting this to 



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» The affinities of the Filicinea?: Bot. Gaz. Jan., 1890. 



