334 PHYSIOLOGY OF GROWTH AND CONFIGURATION 



cent, solution of sugar with gelatine enough to form a jelly. The dark area in the 

 center represents a mass of diastase, toward which the growing filaments are 

 attracted. 1 



It appears that there are substances in the flowers of some plants that pre- 

 vent fertilization by pollen from the same individual, thus resulting in self-ster- 

 ility. If the pollen is applied to the stigmas of another individual of the same 

 species, however, fertilization is not thus prevented. 2 In such cases the pollen, 

 to be effective, must be applied to an individual of different sexual origin from 

 the one that bore it. 



Parthenogenesis is also controlled by external conditions. Nathansohn, 3 for 

 instance, succeeded in obtaining parthenogenetic reproduction in several species 

 of the genus Marsilia by subjecting the spores to high temperatures. 



Higher plants may propagate themselves vegetatively, by means of tubers, 

 bulbs, etc. An organ, or even a portion of an organ, removed from the plant, 

 may generate a new individual. 4 For instance, if a Begonia leaf is cut off and 

 laid upon moist sand, adventitious roots are formed and a new leafy branch 

 develops. If the leaf is taken from a plant that is in bloom, the branch that 

 develops bears flowers instead of being leafy. Fig. 172 shows a leaf of 

 Achimenes haageana that was taken from a plant just about to bloom; flowers 

 have been developed instead of leaves. 5 Leafy branches or flowers may be 

 obtained at will, by cutting the leaves for propagation from plants in the proper 

 stage of development. It thus appears that the leaves of a plant about to 

 bloom contain different chemical substances from those found in the leaves of 

 earlier developmental stages. 6 



The ancient Greeks were already aware that if a bud is taken from one plant 

 and grafted upon another a new branch is produced by the development of the 

 bud, and that this branch retains the special character of the plant from which 

 the bud originally came. The operation of grafting, known to gardeners for so 

 long a time, furnishes the physiologist with a valuable means for studying the 

 processes of growth and metabolism. Vochting 7 has collected the scattered 



1 Lidforss, Bengt, Untersuchungen uber die Reizbewegungen der Pollenschlauche. Zeitsch. Bot. I : 

 443-496. 1909. 



2 Correns, C, Selbststerilitat und Individualstoffe. Festschr. (84 Versamml.) Deutsch. Naturf. u. 

 Aerzte, med.-naturwiss. Ges. P. 186—217. Munster i. Westf., 1912. 



3 Nathansohn, Alexander, Ueber Parthenegenesis bei Marsilia und ihre Abhangigkeit von der Tem- 

 peratur. Ber. Deutsch. Bot. Ges. 18: 99-100. 1900. 



* Goebel, K., Ueber Regeneration im Pflanzenreich. Biol. Centralbl. 22: 385-397, 417-438, 481-505. 

 1902. [In this connection see also; Loeb, Jacques, Rules and mechanism of inhibition and correlation in 

 the regeneration of Bryophyllum calycinum. Botgaz. 60: 249-276. 1915. Idem, Further experiments on 

 correlation and growth in Bryophyllum calycinum. Ibid. 62: 293-302. 1916. Idem, On the association 

 and possible identity of root-forming and geotropic substances or hormones in Bryophyllum calycinum. 

 Science, n. s. 44 : 210-211. 1916. Idem, Influence of the leaf upon root formation and geotropic curvature 

 in the stem of Bryophyllum calycinum, and the possibility of a hormone theory of these processes. Bot. 

 gaz. 63 : 25-50. 1917. Idem, A quantitative method of ascertaining the mechanism of growth and of in- 

 hibition of growth in dormant buds. Science, n. s. 45: 436-439. 1917. Idem, The chemical basis of re- 

 generation and geotropism. Ibid. 46: 115-118. 1917. Idem, The organism as a whole. X + 153 p. 

 New York, 1916.] 



6 Goebel, Karl E., Organographie der Pflanzen, inbesondere der Archegoniaten und Samenpflanzen. 

 Jena, 1898-1901. Part I, p. 41. [Idem, Organography of plants especially of Archegoniatae and Sper- 

 maphyta. Translated by Isaac Bayley Balfour. 2v. Oxford, 1900-1905.] 



6 Klebs, Georg, Ueber die Nachkommen kiinstlich veranderter Bluthen von Sempervivum. Sitzungsber 

 (math.-naturw. Kl.) Heidelberg. Akad. Wiss. 1909 6 : 1-32. 1909. 



7 Vochting, Hermann, Ueber Transplantation am Pflanzenkorper. Tubingen, 1892. 



