FORMATION OF ORGANS AT THE VEGETATIVE POINT 41 



IV. 



NORMAL FORMATION OF ORGANS AT THE VEGETATIVE 



POINT AND REGENERATION. 



The manner in which organs are laid down at the vegetative point 

 requires no comprehensive exposition here l . I may however note the 

 following chief facts : 



1. On vegetative points, whether these be terminal or intercalary, 

 which have an unlimited capacity of growth, the primordia usually arise in 

 progressive serial succession ; they are 



lateral outgrowths, exogenetic or endo- 

 genetic. In many cases, for example 

 monocotyledonous embryos and the 

 Lemnaceae, a clearly limited vege- 

 tative point generally does not exist -. 



2. In the flower-region the vege- 

 tative point is sometimes completely 

 used up in the formation of the leaf- 

 organs arising latest from it. Members 

 in this case are terminal. A like 

 condition is found in the development 

 of the antheridia and archegonia of 

 many mosses. 



3. On shoot-axes which have 

 limited growth, and in primordia of 

 leaves, the direction of the serial 

 succession of the primordia of organs 

 depends upon what part of the vege- 



FlG. 1 8. Vallis'ieria (Lagarosiphon) alternifolia. 

 Longitudinal section of a young inflorescence. The 

 flowers are laid down in descending serial succession. 



tative point retains longest its embryonic character. If this part should 

 be at the base then the serial succession of the development is basipetal 

 (see Fig. 18), or, as is the case with the primordia of the lateral leaflets 

 in many leaves, as well as with the ovules upon some placentas, the 

 development proceeds from the middle to the apex and base. Intercalation 

 of new primordia of organs between those already existing takes place 

 amongst the higher plants only in the region of the flower. 



1 Compare the chapter upon this subject in my ' Vergleichende Entwicklungsgeschichte der 

 Pflanzenorgane,' p. 177. 



2 See Part II of this book. 



