CHAPTER VI 

 DEVELOPMENT AND REPRODUCTION 



§1. Influence of External and Internal Conditions on Development.— The 



form and the arrangement of the parts of plants are dependent upon external 

 conditions to a very marked degree. According to the conditions under which 

 they develop, plants vary in their external form as well as in their internal 

 structure, and many peculiarities in configuration that appear to be 

 brought about solely by internal conditions are mainly the result of the ex- 

 ternal conditions that prevailed during the period of development. It has al- 

 ready been seen (Part II, Chapter III) that each external condition— such as 

 heat, light, atmospheric pressure, humidity, gravitation, and the supply of 

 nutrient material — exerts an influence upon plant growth, and consequently 

 upon both external form and internal structure. This influence is of course 

 more pronounced when a number of different environmental conditions affect 

 the plant simultaneously, as is the case; in nature. For example, the climato- 



FiG. i6i. — Achyropkorus quitensiSr an alpine plant. (^ natural size.) 



logical conditions of high mountains are very different from those of lowlands, 

 and alpine plants differ in a corresponding way, in form as well as in structure, 

 from those growing at lower levels.' The predominating plants of high moun- 

 tains have more or less reduced stems, relatively large, rigid leaves, and large, 

 brightly colored flowers. Fig. i6i represents a specimen of Achyropkorus 

 quitensis, a plant with well-developed alpine characteristics, found at altitudes 

 of from 3000 to 4000 m. in the Andes, from Colombia to Peru. 



The experiments of Bonnier^ have shown that many of the peculiarities of 



1 Wagner, A., Zur Kenntnis des Blattbaues der Alpenpflanzen und dessen biologischen Bedeutung . 

 Sitzungsber. (math.-naturw. Kl.) K. Akad. Wiss. Wien loi^: 487-548- 1892. 



2 Bonnier, Gaston, Cultures exp6rimentales dans les Alpes et las Pyr6n6es. Rev. g^n. bot. 2 : 513-546. 

 1890. Weinzierl, Theodor, Ritter von, Der alpine Versuchsgarten auf der Vorder-Sandlingalpe bei Aussoe, 

 und die daselbst im Jahre 1890 begonnenen Samenkultur- und Futterbauversuche. Landw. Versuchsst. 

 43: 27-126. 1894- 



28s 



