310 Nutrition luuI Sclcctio)i. 



follow rapidly on one another. But if the conditions are 

 iinfa\orable, as in a room, differentiation proceeds more 

 slowly. The internodes tend to become abnormally long, 

 to produce too little wood, the leaves develop small pin- 

 nules only, and in very unfavorable conditions I have 

 sometimes observed an interruption in the series of leaf- 

 forms on the stem. Above the lyrate leaves simple ones 

 were again formed, the series turning backwards.^ 



These phenomena are much better illustrated in those 

 cases in which the first leaves are more compound than 

 the later ones; for instance in the species of Acacia which 

 produces phyllodes in reference to which Goebel's im- 

 portant investigations have thrown so much light on the 

 relation between embryonic forms and external condi- 

 tions.- I have already referred to this above; but I 

 might now mention a figure of a seedling of Acacia 

 verticillata which, after it had already reached the stage 

 of producing phyllodes, was induced to repeat the bi- 

 pinnate form of the embryonic leaves by unfavorable 

 conditions. In the same w^ay the production of linear or 

 arrow-shaped leaves of Sagittaria sagittifolia and that 

 of the perforated leaves of Monstera dcliciosa and others 

 was shown to be dependent on external conditions. In- 

 sufficient nutrition tends to bring about a recurrence of 

 tlie embryonic form, and it seems to be a secondary 

 (|uestion whether this is the simpler or the more com- 

 plicated. The Campanula rotund i folia studied by Goe- 

 BEL, the flowerstalk of which changed from the linear 

 to the heart-shaped form of leaves,^ is perhaps the best 



^ See also E. Roze, La transmission des formes ancestralcs dans 

 Ics vcgetaux, Journ. d. Bot., Annee X, Nos. i and 2, 1896. 



^ K. GoEBEL, Organogra-phie der Pflanzen, I, p. 150. Fig. 105. 



' GoEBEL, Flora, 1896. Vol. LXII, Pt. I. 



