DIFFERENCES IN THE FORMATION OF 



ORGANS AT DIFFERENT DEVELOPMENTAL 



STAGES. JUVENILE FORMS 1 



INTRODUCTION. 



ALL living beings are, as is well known, in a condition of continual 

 change unless they are in that state known as ' latent life,' and we have 

 in this section to consider the outward changes of configuration which are 

 associated with this changing condition. As a rule these are more 

 manifold the higher the organization exhibited by a plant. In lower 

 plants in which a separation of generative from vegetative plasm has not 

 yet appeared, Bacteria and Conjugatae for example, the changes of form 

 in the course of development are very simple, but in the more highly 

 differentiated plants there is bound up with the formation of the sexual 

 propagative organs a climax of development which corresponds in a 

 certain degree with the ' climacteric ' of animals, in that the vegetative 

 parts die off sooner or later, although in some trees which are not 

 exhausted by the formation of seeds the numerous vegetative points may 

 theoretically be regarded as having unlimited existence. In these cases 

 it has rightly been considered that external unfavourable conditions are 

 responsible for the fact that a gradual cessation of vegetation takes 



1 At p. 251 of my ' Vergleichende Entwicklungsgeschichte der Pflanzenorgane ' I have given 

 an account of the subject treated of in this chapter, and further information will be found in 

 my papers ' Uber die Jugendzustiiude der Pflanzen ' in Flora, 1889, p. I, and ' Uber Jugendformen 

 von Pflanzen und deren kiinstliche Wiederhervorrufung ' in Silzungsberichte der kgl. bayer. Aka- 

 demie der Wissenschaften, math.-naturw. Classe, 1896. The literature, so far as it relates to 

 Spermaphyta, is collected by C. Schiiffer in his treatise ' Uber die Verwendbarkeit des Laubblattes 

 der heute lebenden Pflanzen zu phylogenetischen Untersuchungen,' in Abhandl. aus dem Gebiete 

 der Naturwissenschaften, henvusgegeben vom naturwissenschaftlichen Verein, Hamburg, Bd. xiii 

 (1895). 



