18S CONCLUDING KEMARKS AND Cuai-. IX, 



organs — yot the tendency differs greatly m different 

 species, and is variable in degree in the individuals oi 

 the same species, as may be seen in almost any pot 

 of seedlings of a long cultivated plant.* There is 

 therefore a basis for the modification of this tendency 

 to almost any beneficial extent. That it has been 

 modified, we see in many cases : thus, it is of more 

 importance for insectivorous plants to place their 

 leaves in the best position for catching insects than 

 to turn their leaves to the light, and they have 

 no such power. If the stems of twining plants were 

 to bend towards the light, they would often be drawn 

 away from their supports ; and as we have seen they 

 do not thus bend. As the stems of most other plants 

 are heliotropic, we may feel almost sure that twining 

 plants, which are distributed throughout the whole 

 vascular series, have lost a power that their non- 

 climbing progenitors possessed. ]\Ioreover, with Ipo- 

 mcBa, and probably all other twiners, the stem of the 

 young plant, before it begins to twine, is highly helio- 

 tropic, evidently in order to expose the cotyledons or 

 the first true leaves fully to the liglit. With the Ivy the 

 stems of seedlings are moderately heliotropic, whilst 

 those of the same plants when grown a little older 



* Sh-iisbnrgev has shown in Ill's theliglit. Some indivkluals, more- 

 interesting work ('Wirkung des over, appear to be iiidiiferent to 

 Lichtes . . . aiif Sehwarmspnreii,' tlie light; and those of different 

 1878), that the movement of the species behave very differently, 

 swarm-spores of various lowly 'I'lie brighti-r the light, the 

 organised plants to a lateral light striiighter is their course. They 

 is influenced by their stage of exhibit nlso for a short time the 

 development, by the temporatuio afler-effccts of light. In all these 

 M which they are subjected, by n sp. ols Ihey reemble the higher 

 the degree of illumination under plants. See, also Sinhl ' Ueber 

 which they have been raised, and den einfluss der Lichts'auf die 

 , by other unUnown causes ; si. that Bewcgungs - erscheinun'^eii del 

 the swarm-spores of the same Sohwarmsporen ' Verb °d phvs- 

 species may move across the field mod. Geselsshulft in Wii'rzburo- 

 ol the mifrosa^pe either to or from li. xii. 1878. 



