164 COOK 



like Archidium are also annual and each plant is normally 

 fertile, but among the higher mosses fruiting is often deferred 

 till a considerable number of plants, often a whole tuft, has been 

 formed by vegetative propagation. The same is true among 

 the ferns, and in many different families of tiie flowering plants. 

 It is accordingly not unreasonable to think of the cotyledons 

 as multiplying, after vegetative growth has commenced, to form 

 a poly-cotyledonary, leafy axis, with the spore-bearing functions 

 restricted to the upper members of the series, just as many ferns 

 produce spores only on a few small specialized fronds. The 

 formation of a compound plant by adding units one above an- 

 other is simpler and more direct than the budding out of lateral 

 shoots from lower down, like those which form roots and root- 

 stocks. The successive members of the series have the same rela- 

 tions to each other as the original basal unit might have had to its 

 parent plant, or as the vegetative capsules of Anthocei'os and of 

 the mosses still have. The jointed internodal structure which 

 characterizes the stems of angiosperms is itself a distinct intima- 

 tion that the plant-body in this group has been made up in a 

 manner essentially different from that of the comparatively joint- 

 less stems of higher pteridophytes and conifers. That the 

 plumule may be viewed as an outgrowth from the cotyledons, 

 instead of being a predetermined structure to which the coty- 

 ledons are accessory, is indicated by the fact that in some plants 

 there is more than one plumule, and that in others, such as the 

 cotton plant, buds many arise in the axils of the cotyledons, and 

 in others still, small pieces of the cotyledons can produce 

 plumules.^ 



It is also noteworthy that other internodes, like the cotyledons, 

 grow by intercalation, or at the base, instead of at the apex, the 

 terminal bud having been laid down in advance, like the plumule, 

 before the expansion of the internode begins. This principle 

 of intercalary growth is illustrated most strikingly, perhaps, in 

 the palms, in which not only the internodes themselves, but 

 their leaves and inflorescences are definitely constructed from 



' Mr. A. J. Pieters informs me that in several species of Plantago pieces of the 

 cotyledons have the power of producing new plumules and root-hairs from the 

 cut surface, and that perfectly normal plants have grown to maturity from such 

 new-formed plumules. 



