PROGRESSIVE STAGES IN COMPLEXITY OF STRUCTURE. 



591 



ments are again divided, and from the single compartments (i.e. cells) originate 

 here plate-like, there mass-like complexes, in this place cell-rows, in that cell-nets; 

 these, however, are not isolated, but remain joined and produce small, wonderfully- 

 arranged structures. The result of this modelling process is therefore a plant- 

 member composed of varied cell-complexes, with a definite internal structure, with 

 definite external contour, and also with entirely definite functions in the economy 

 of the plant. In spite of the variety of shape which plant-members, formed 

 from various constituent cell-tissues, exhibit in the many thousands of plant- 

 species which develop into bodies, they can yet be referred to a few fundamental 

 forms, viz., to the leaf, stem, and root. These members of the plant-body are in 



4 d " ~ 5 6 



Fig. 140.— Liverworts with Cell-nets, Cell-plates and Cell-rows in various transitional forms. 



^ Jungermannia pumila. « Jungermannia quinquedentata. « Polyotus magellanicus. * Ptilidium ciliare. * Trichocolea 

 tomentella. « Jungermannia trichophylla. (All the figures magnified.) 



most cases so arranged that a stem represents the starting-point and support of 

 many leaves and roots. In the simplest form the plant-body appears as embryo 

 and as bud. The latter consists of a very short stem, beset with leaves lying 

 closely above one another, and grows later into a shoot which agrees in structure 

 with the parent plant producing the bud, of which it actually forms a replica. 

 If the young body remain connected with the old, it is called a branch; the 

 branches may again form buds, and these, again, twigs; and in this way originate 

 much-branched plant-structures which often attain to considerable dimensions, 

 and must be regarded as compound. In rare instances the laterally-inserted buds 

 are detached from the body producing them, before they develop further; and 

 these buds, which are known as bulbils, give rise to an independent plant-body. 

 This process reminds one of the swarm formation of cell-complexes which has 

 been spoken of above. 



This is also the place to notice the analogy between vegetable and animal 



