Studies in Californian Hepaticae. I. Asterella californica

Abstract

1. Asterella californica, the commonest species in California, served as the basis for the present investigation, but was supplemented in part by observations on A. palmeri. 2. The fleshy, dichotomous thallus grows by means of a single, large cuneate apical cell. The ventral surface bears two rows of appendaged scales, and both smooth and pegged rhizoids. 3. The green tissue is loose and extensive. The air chambers, lacking chlorophyllose filaments, arise schizogenously, the split starting at the surface of the thallus. 4. The air pores are simple on the thallus and male receptacle, and barrel-shaped on the female receptacle. 5. The male receptacle represents a simple dorsal upgrowth of the thallus, the female receptacle a definite branch system, the apical cell of the thallus being involved in its formation. Most commonly four growing points are organized on the latter, and later four conspicuous lobes develop. Ordinarily two or three archegonia arise in each group. 6. Following the formation of a young carpocephalum, a new growing point may appear beneath it at the posterior inner margin of each wing and just in front of the groove in the receptacle stalk. These continue the vegetative growth of the thallus, the receptacle thus appearing to arise from the bottom of a dichotomy. 7. Evidence is presented suggesting that these growing points are adventitious in origin and bear no relation to the original apical cell of the thallus. 8. The development of the antheridium is essentially similar to that of other Marchantiales. Several deviations from the normal sequence of early wall formation are described. 9. Early development of the archegonium presents no unusual features. The ventral canal cell and egg are differentiated after four neck canal cells are formed, but this number is then increased to eight. 10. Before any vertical walls appear, the embryo of Asterella palmeri undergoes transverse divisions which result in a filament of four cells. It seems likely that this develops by a transverse division of both hypobasal and epibasal segments of the fertilized egg. 11. It is suggested that the lowest cell of the young embryo gives rise to the foot, the next one to the seta, and the upper two to the capsule.