Lecture XVII. 131 



The different grades of its concentration occurring in the grooves 

 of the archegoniophore lead the sperms on among the rhizoids 

 until they reach the archegonial patch. There they are set free 

 among the archegonia and are attracted to an archegonium, the 

 neck of which has just opened. One passes in and fuses with the 

 ovum. 



Thus it is evident that while the vegetative parts of this plant 

 are largely suited to a terrestrial life the ciliated sperm-cells require 

 aquatic conditions in order that they may function and carry on 

 fertilisation. 



This is only possible by special arrangements which secure a 

 water connection between the two branches supporting the sexual 

 organs. The development of an internal conducting system by 

 the superficial rhizoids is a point of great interest, and it is obvious 

 that in addition to transmitting the sperm-cells, the rhizoids of 

 the two sexual branches must play an important part in conveying 

 water from the soil to the upper regions of these branches, 

 bringing up supplies needed in growth and making good the water 

 lost in evaporation. 



The spherical oosperm formed by the fusion of the sperm with 

 the ovum in the archegonium does not forthwith develop into a 

 plant of Marchantia. It divides into eight segments. Four of 

 these lie round the pole turned towards the neck and four round 

 that next the base of the archegonium. These latter by further 

 subdivisions and growth, form a little mass of tissue which presses 

 itself into the base of the archegonium and acts as an absorbing 

 organ (called the foot), and as the stalk of the developing embryo. 

 The distal hemisphere enlarges more rapidly and is soon differ- 

 entiated into a thin outer layer of cells forming the wall of a 

 capsule and containing a vast number of polyhedral cells fitting 

 closely together. * Some of these cells elongate rapidly and develop 

 tubular walls tapering to each end. Their protoplasm disappears 

 after it has deposited spiral thickenings on the inside of the cell- 

 walls. These are elaters. The others are completely filled with 

 protoplasm. Their nucleus is large, and soon divides into four. 

 Round the four resultant nuclei the cytoplasm separates, and so 

 four globular cells (spores) are formed simultaneously in each 

 mother-cell. They are arranged tetrahedrally in the mother-cell 

 and are slightly flattened on three faces by mutual pressure. The 

 outer surface of the walls of these spores is covered with a finely 

 granular deposit from the remains of the protoplasm of the 

 mother-cell. 



During the development of the embryo into the spore-capsule, 



9* 



