28 



Göte Tnresson 



After an exposure of three hours the erect forms of Ä. pululaiii and A. lali- 

 folium are found to be still growing upwards, while their prostrate races have 

 already begun to move downwards towards the horizontal position. Prolonged 

 exposure is necessary to induce the downward movements in the normally erect 

 forms, as is shown in the table. AtripJex litorale seems to be the least sensitive 

 of the last three species tested. 



Table XV. 





0 hours 



3 hours 



5 hours 



1 



A. pat. erectum 



14, 

 11, 9 



+ 4 



+ 4, + 6 



— 5 



-6,-6 



2 



A. pat. prostratum.. 



18, 25 

 5, 26 



-5,-7 

 — 4,-2 



— 11, — 6 



— 15, — 2 



3 



A. prostratum Bouch. 



23 

 3, 39 



— 15 

 — 2,-16 



— 7 

 — 4,-11 



4 



A. lat. erectum 



50 

 3, 33 



+ 5 

 + 11, + 5 



— 3 

 -1,-4 



5 



A. lat. prostratum... 



1 



1, 12 



— 4 



-1,-3 



— 7 



-9,-5 



6 



A. Babingtonii 



10 



3, 47 



+ 8 



+ 1, + 0 



+ 0 



- 1,-6 



7 



A. hastatum 



1, 26 

 13, 48 



+ 1, + 4 

 + 7, + 18 



+ 0,-4 

 -2,-2 



8 



A. litorale 



28 

 20, 32 



+ 5 

 + 5, + 6 



— 2 

 ±0,-2 



The ecological significance of the differing degree of photocliny is easily 

 understood when the natural habitats of the different species of the genus Afriplex 

 are compared. The most pronounced photocliny among the shore-species is shown 

 by A. prostratum Bough., which on the beach reaches its maximal distribution in the 

 belt most strongly exposed to sun and wind, viz. the upper snpralittoral. It is 

 expelled from other less exposed localities by its more robust but less photoclinic 

 congeners. A. litorale illustrates the same fact. On the much exposed west side of 

 Hallands Väderö not a single specimen belonging to this species is found, although 

 suitable substratum is found in several places. However, on the sheltered east side 

 of the island extensive areas are covered with this species, and here it attains 

 gigantic dimensions. A. patulum is rare on the beach, the reason of this being not 

 yet understood. But the prostrate race of the species, which is also known under 

 the name of A. patulum var. angustifoliuin J. E. Sm. has, nevertheless, succeeded 

 in finding a habitat most, suitable for its needs. I mean the stubble-fields. The 

 flora of our stubble-fields is a characteristic selection flora, which in the southern 

 parts of Sweden includes in addition to the plant under discussion Anagallis, Odon- 

 tites, Euphorbia exigua, Stachys arvensis and other annuals low in stature. Thanks 



