Newcombe Sensitive Life of Asparagus plumostis. 35 



geonasty, as well as diageotropism; but the later writings 1 ) show 

 a tendency to refer the change in most plants to diageotropism 

 alone, this diageotropism being, in many cases, induced by light. 

 I fail to find anywhere in the literature a case in which the 

 plagiotropic declination of a formerly orthotropic shoot may not 

 be induced by the action of light. In the seedlings of Asparagus 

 plumosus, however, we have such aninstance. Raised in darkness 

 from the seed, the aerial shoots make as great*a declination as tho 

 raised in the light. The angles of declination run usually from 

 45° to 90°; only one of my 14 seedlings showed its declination 

 less than 45°. These angles are about the same as made by 

 seedlings grown in the light; for while the declination of shoots 

 growing from rhizomes is almost invariably 90°, that of normal 

 seedlings is, in perhaps half of the number, less than 90°. 



This prompt bending of the seedling shoot into the plagio- 

 tropic position in the dark was a surprise to me. One may assume 

 that in phylogeny the appearance of this curve is secondary. 

 Hence, on the principle that the seedling resembles, more or less, 

 ancestral forms, one might expect the seedling in the dark to grow 

 erect. The taking of the plagiotropie position in the dark under 

 apparently the sole influence of gravitation might be interpreted 

 as an inheritanee, and the change of attunement to gravitation 

 might be regarded as due to a phasogenicekphory 2 ) related to the 

 approaching cessation of growth. 



Altho it is evident by Observation of seedlings kept always 

 in the dark that light can have little if anything to do with the 

 diageotropic position assumed by them, it is just as evident that 

 light has considerable influence on the establishment of the dia- 

 geotropism of shoots grown from rhizomes. It has been pointed 

 out that the young orthotropic shoot of Asparagus, growing in 

 light, usually has its vertical plane of curvature determined by 

 the direction of light; that is, the positive heliotropism of the shoot 

 keeps the tip more or less declined for a week or more before the 

 diageotropism makes itself evident, and then the diageotropic decline 

 is in the same vertical plane as the former heliotropic bend. This 

 determination of the vertical plane of curving by light is exactly 

 what takes place, according to Czapek 3 ), in the normal declination 

 of the epicotyl of Cucurbita pepo. But this is not the only effect 

 of light in this phenomen. By reference to the part of this paper 

 under the caption, „Behavior of Shoots never in Light", it will be 

 seen that without light, the shoots never attain a fixed plagiotropic 

 position. They begin to make the plagiogeotropic decline in the 

 dark, they may decline 15°, 30°, 45° or rarely go nearly to the 

 horizontal, but after a pause of a few hours or a few days, they 

 invariably erect themselves again to the vertical direction. And 



!) Czapek, Weitere Beiträge zur Kenntnis der geotropischen Reiz- 

 bewegungen. (Jahrb. wiss. Bot. XXXIII. 1898. p. 175.) — Mai ge, 1. c. 



2 i Semon, Die Mneme. Engelmann, Leipzig 1908. 



3 ) Czapek, Studien über die Wirkung äußerer Reizkräfte auf die Pflanzen- 

 gestalt. iFlom. 85. 1898. p. 424.) 



3* 



