LECTURE IV. 



THE TYPICAL FORINIS OF SHOOT OF THE VASCULAR PLANTS. 



We distinguish, generally, as the shoot, the vegetative organ standing in op- 

 position to the root. There are, it is true, derived (metamorphosed) forms of shoot 

 which live hidden in the substratum, as there are indeed derived forms of root also, 

 which, abandoning their primitive characters, become developed outside the nutri- 

 tive substratum. The primary and most prominent peculiarity of the shoots, however, 

 is that they raise themselves above the substratum, in order to fulfil their most important 

 vital function in the air (occasionally in water) under the influence of light, that 

 is, to decompose carbon dioxide by means of their chlorophyll, and to pro- 

 duce organic substance, from which new shoots and new roots may be formed. 

 A second function of the shoots, perhaps as essential, consists in that earlier or later 

 they bear the proper reproductive organs, viz. the sporangia and sexual organs, 

 wWch are never formed on roots. 



The mode of life, outward form, and internal structure of the shoot depend 

 upon the way in which, according to circumstances, these two main problems, as- 

 similation and the development of reproductive organs, are solved. In many cases, 

 it suffices that the shoot containing chlorophyll simply rises above the substratum 

 to the light ; it then assimilates, and subsequently developes the reproductive organs. 

 Generally, however, a further division of labour appears within .a shoot or .shoot- 

 system ; some branches, as subterranean shoots, store up the products of the as- 

 similation of those above ground, and become transformed into reservoirs of reserve 

 material, while, very often, certain branches are specially entrusted with the formation 

 of reproductive organs. That roots also may arise on the shoots, according to their 

 mode of life, has already been mentioned several times ; they represent, therefore, 

 the proper body of the plant, on which all other organs appear, as the limbs on the 

 trunk of an animal. 



These deviations from the primitive nature of the shoot, and its metamorphoses 

 and reductions, go much further, and are far more various than in roots, and 

 it is not so easy as with the latter to express the fundamental physiological 

 character clearly and exhaustively. It will be the object of later lectures to give clear 

 ideas of this enormous variety of the development of shoots, by a series of examples. 

 To-day, however, we shall confine ourselves exclusively to the peculiarities of typically 

 developed shoots, as they occur in the great majority of vascular plants. What tl.e 



