INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 991 



formed by particular portions of the epidermis becoming covered by 

 the more rapid growth of the adjoining parts. The process is, in 

 fact, the same as in the formation of the sexual organs. The author 

 is of opinion that the pores and canals are primary, the air-chambers 

 secondary formations, notwithstanding the occurrence of apparent 

 deviations, as in Marcliantia. 



AVith respect to the filling up of the air-chambers, they may 

 remain altogether empty, as in Sauteria and Oxymitra. But more 

 frequently segmented rows of cells proceed both from the basal inner 

 wall and from the lateral walls, running towards the covering of the 

 air-chamber ; this occurs in Marcliantia, Preissia, Lunularia, and 

 Fegatella. Finally, as in liehoulia, rows of cells grow out into the 

 air-chamber from all the inner walls of the cells which bound it, 

 including the covering while in process of formation, thus dividing it 

 into a number of imj)erfect chambers. 



Inflorescence of the Marchantiaceae.* — The inflorescence of the 

 MarchantiacciD takes the form of disks sessile upon the thallus or of 

 umbels elevated above it on a pedicel. The best-known examples are 

 the male and female inflorescences of the genera Marcliantia and 

 Preissia. It has long been held that these receptacles and their 

 pedicels must be regarded as metamorphosed foliar axes ; as is shown 

 by (1) the remarkable coincidence in structure of the dorsal side of 

 both male and female receptacles with that of the corresponding side 

 of the sterile part of the thallus ; (2) the altogether similar dorsi- 

 ventral development of the pedicels to that of the thallus ; (3) the 

 aerial layer and stomata which continue without interru])tion from 

 the thallus to tlie pedicels ; and (4) the ventral or radical channels of 

 the pedicel w'ith their scales, which must certainly be regarded as the 

 equivalent of the ventral side of a portion of the thallus. 



In an exhaustive treatise on the subject, Leitgeb maintains that 

 the attempt to apply this explanation to all the remaining genera of 

 Marchantiacea) with the exception of Targionia, and to regard all male 

 and female receptacles as resulting from the transformation of a 

 branch, is certainly inadmissable as regards most male inflorescences, 

 and is justified only for a portion of the female. 



Leitgeb maintains that tlie Marchantiaceae arc descended from 

 Riccia-likc forms, and that they and the Ricciea) belong without 

 doubt to one and the same series of development. The following are 

 the most important points relating to the develoiiment and position of 

 the reproductive organs of the Iticciea) : — 



1. Both kinds of sexual organs have their origin immediately 

 behind the growing apex. Henco they invariably stand on the dorsal 

 side next the median line of the thallus, on the mid-rib, and are 

 developed in acropetal succession ; new organs never being formed 

 further from tlie apex tlian those already in existence. 



2. The mother-cells of the sexual organs at first project like 

 papilla) al)ovo tlio surface ; in conseciucncc of the increase in thick- 

 ness of the thallus, they subsequently ajjpcar as if imbedded in the 

 tissue. 



* Si;, k. Akad \Vi.-^s. Wini,' Ixxxi. (1880) | p. 12:5-13. 



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