1897] FUNDAMENTAL PRINCIPLES OF HEREDITY 309 



extraordinary powers of propagation of the Moss-plant : if cut up 

 into fragments, almost any green cell, whether of the Moss-plant or 

 the young urn, is capable of growing out into a green filament that 

 will produce new leafy plants ; and this is in addition to the propa- 

 gative power by ordinary branching or budding of the embryonic 

 tissues at the growing point. We will, according to custom, begin 

 our table with the coupled-cell. 



It will be seen here that there is no necessary colonial death (as 

 in Volvox) of the leafy Moss-plant, though the older tissues of the 

 stem and the leaves usually die down after the maturation of the 

 parasitic capsule, and that the power of propagation possessed under 

 certain circumstances by the green cells of the Moss-plant and urn 

 make them possible direct ancestors of reproductive cells. 



Still, in what we may regard as the normal cycle, the repro- 

 ductive cells produce among their offspring collaterals as well as 

 direct ancestral forms. The character of the cycle is noteworthy ; 

 two systems of colonial growth each beginning with a single cell 

 are determined or closed by the production of brood mother-cells; 

 and these systems contrast both in the characters of the colony and 

 in the nature of the brood-cells. The colonial outcome of the spores 

 is the filamentous growth and the leafy Moss-plant, and the brood- 

 cells formed therefrom are the sexual pairing-cells; the colonial 

 outcome of the coupled-cell is the capsule, and its brood-cells are 

 the asexual spores. This is then an ' alternation of generations ' in 

 the sense of colonial or habitual terminology. Botanists have termed 

 the contrasting colonial plants ' Sexual ' and ' Asexual,' Gametophyte 

 and Sporophyte, respectively from the character of the brood-cells 

 which each produces in turn. 



In the ascending scale of the Vegetable Kingdom we first meet in 

 the Moss-plant with those tissue-cells which we term 'embryonic' ; 

 these must be defined as colonial cells nourished by the adult part 

 of the colony, and having for their sole function growth or con- 

 tinued division at the limit of growth to form new cells and organs. 

 Such cells are obviously not at all ' primitive,' as they are fre- 

 quently called, but on the contrary are the essential outcome of 

 high colonial differentiation. That the whole colony may exist in 

 this condition in the early stages of development is only rendered 

 possible in the ease of the Moss-urn by its receiving nourishment as 

 a parasite from the leafy plant. 



The Fern is only comparable with the Moss by a complete 

 detachment from preconceived ideas. Most readers know that 

 the Fern sheds from the brown ridges or spots on the under side 

 of its leaves a fine dust, whose particles are the spores. Each 

 spore in germinating produces a cellular filament, which soon 

 expands into a green plate, the equivalent of the leafy Moss- 



