No. 551] 



NOTES AND LITERATURE 



tiera and Marchantia. The latter genus is the most highly spe- 

 cialized of all the Marehantiales. 



The Jungermanniales 

 Much the greater number of liverworts belong to the Junger- 

 manniales. The classification of this large order is very much 

 in need of revision, as it is at present in a very unsatisfactory 



They are generally divided into two series of very unequal size, 

 this division being based upon the position of the archegonium 

 — and are denominated the Anacrogyna? and Acrogyna?. In the 

 former the growing point of the shoot persists indefinitely, while 

 in the latter, in the fertile shoots, it is sooner or later trans- 

 formed into an archegonium, and the sporogonium is therefore 

 terminal. 



The name Metzgeriaceaa was later proposed by Underwood, as 

 a substitute for Leitgeb 's Anacrogyna?, the Acrogynce being alone 

 called Jungermanniacese. Cavers thinks these two divisions are 

 largely artificial, and it must be admitted that there is much to 

 be said for his view. 



Comparing the Jungermanniales, as a whole, with the Mar- 

 ehantiales, it is seen that in the former specialization has been in 

 the direction of external differentiation, i. e., in most of them a 

 more or less definite axis, bearing leaves, is present, but the tis- 

 sues remain quite uniform. In the Marehantiales, on the other 

 hand, the plant is a thallus, but the tissues are of various kinds. 



The simplest of the Jungermanniales, e. g., Aneura, Pellia, 

 etc., have a very simple thallus, either composed of quite similar 

 cells, or with a midrib which may possess a strand of special 

 conductive tissue. The simplest type of thallus is quite like that 

 of Sphcerocarpus, and may very well have originated from some 

 similar type. 



In these thallose Jungermanniales there is frequently a tend- 

 ency toward the development of marginal lobes, which may bear 

 a quite definite relation to the primary divisions of the single 

 apical cell of the thallus. Such marginal lobes are undoubtedly 

 homologues of the leaves found in the more highly specialized 

 leafy liverworts— the ' ' Acrogyme, ' ' of Leitgeb. Sometimes these 

 leaf -like organs of the anacrogynous liverworts are very distinct, 

 as in Treubia, and the transition to the typical leafy liverworts 



