142 SECOND GROUP —MUSCINEAE. 



the sexual organs, especially in the leafy species. Besides these forms of envelope the 

 Hepaticae (not the Mosses) have often another called the pen'gym'um, which grows up 

 as a circular wall from the thallus at the base of the archegonia, and at length 

 surrounds them like an open sac. 



The ASEXUAL GENERATION {sporophore, sporophyle, the moss-fruit or 

 sporogo7u'u»i) is formed from the oospore in the archegonium : by repeated cell- 

 divisions it is transformed into an ovoid embryo and grows at its apex, which is the 

 pole turned towards the neck of the archegonium. 



The sporogonium lives almost entirely at the cost of the vegetative body on 

 which the archegonium is placed ; it is physiologically the asexual, spore-producing 

 generation, and parasitic on the sexual generation. The venter of the archegonium, 

 in which the oospore lies, grows broader as it follows the growth of the embryo, and 

 in this condition is called the calyptra. In Rucia, the lowest form in a series of 

 Hepaticae, namely the Marchantiaceae, the sporogonium remains all its life inclosed 

 in the calyptra. The spores are set at liberty by the decay of that portion of the 

 thallus in which the sporogonium is immersed. In other Hepaticae also the embryo, 

 the young sporogonium, passes the larger part of its existence in the venter of the 

 archegonium. In Pellia epiphylla, for exam[)le, one of the most common of our 

 thalloid Jungermannieae, the sexual organs are ripe and fertilisation takes place 

 in May. The embryo requires the whole summer for its full development, and by the 

 autumn is in all essential points mature ; but it is not till the next spring that by 

 sudden and vigorous elongation of the stalk it bursts through the calyptra and 

 disseminates its spores, a proceeding which is completed in a few days. In Anthoceros 

 the sporogonium has not so short a life, owing lo the power of intercalary growth at its 

 base ; while ripe spores are being dissemina'ed from its upper part, new ones are being 

 produced below, and this may go on for a long time ; there are foreign species which 

 may in this way dev^lope sporogonia seven centimetres long. In ihe Hepaticae the 

 calyptra is broken through, as we have seen, and remains as a sheath at the base of 

 the sporogonium ; but in the Mosses the elongated fusiform embryo tears the calyptra 

 at the base and carries it up with it in different forms as a cap on its apex. The 

 sporogonium of some Mosses requires more than a year for its full development, as in 

 certain species of Polytrichum, and in Hyp7ium crista caslrensi's. 



The special function of the sporogonium is to produce spores. This function is 

 performed in the simplest manner in Riccta, where the embryo is fashioned into 

 a round cellular body, all the cells in which, with the exception of the layer which 

 forms the wall, become spore-mother-cells producing each four spores. But in the 

 higher forms the sporogonium is made up of distinct parts; z. fool or s/alk, which 

 often thrusts itself into the tissue of the vegetative body, and a capsule in which 

 the spores are formed. The differentiation inside the young capsule into the cells 

 from which the spore-moiher-cells are formed, and the cells which are employed to 

 construct the wall or for any other purpose, takes place very early. The group of 

 cells from which the spore-mother-cells are formed may be named, both here and in 

 the Vascular Cryptogams, the archesporiuvi. This is generally one layer of cells, but, 

 according to Leitgeb, it consists in many of the Jungermannieae of several cell-layers 

 one above another. In Rucia and the Mosses spore-mother-cells only proceed from 

 the archesporium. But in most of the Hepaticae a number of the cells remain sterile 



