Meristems 91 



allometric relationships ( p. 105 ) . The development of a few similar organs 

 of determinate growth has been studied, such as the thorn shoots of 

 Gleditsia (Blaser, 1956). 



In leaves which do not show the usual dorsiventral character but vari- 

 ous, more complex shapes, such as pitcher-like or peltate blades, the 

 origin of these structures is by a system of localized meristems (Roth, 

 1957). These have not been studied extensively and present some impor- 

 tant developmental problems. 



The growth of other organs, such as perianth parts, ovaries, and fruits, 

 resembles that of leaves in showing certain localized differences in rate 

 and direction of growth, but growth is mainly diffuse and nothing com- 

 parable to a true localized meristem is operative save in exceptional cases. 

 Not only are the different dimensions of such an organ clearly correlated 

 in a progressively changing pattern but different parts of the organ, such 

 as blade and petiole, and fruit and pedicel although often growing at 

 different rates, also keep in step with each other. Growth of cer- 

 tain structures, notably the fruit stalk, involves some cambial activity. 



Whatever type of growth a plant organ may show, whether by apical 

 meristems, cambium, or diffusely distributed embryonic activity, it is 

 under strict developmental control. The problem of this control is some- 

 what more complex in a plant, where both diffuse and localized growth 

 occur, than in an animal, where the latter is generally absent. The pres- 

 ence in a plant of these two somewhat different methods of growth offers 

 certain advantages because of the possibility of studying in the same in- 

 dividual two different types of morphogenetic control. However growth 

 occurs, its activities are correlated and not isolated events. 



