Petch : Notes on Aster tripoliiim. 



53 



long-, made up of ovary 2-2*6 mm., tube 3-4*1 mm., bell 2*5- 

 4*2 mm. ; the breadth of the bell (unopened) was slightly more 

 than I mm. In a disc flower of 24 florets the length varied 

 from 8-io"6 mm., made up of ovary 2-2*6 mm., tube 3-4*1 mm., 

 bell 2*5-4*2 mm. In this 12 florets were less than 9 mm. long ; 

 in the first only 2. The dimensions of the florets in the same 

 heads differ therefore, increasing towards the centre, and the 

 florets of a rayed head are, for corresponding positions, longer 

 than those of the discoid head ; there is no appreciable difl'erence 

 in breadth. This is contrary to MacLeod's observation. He 

 says : ' The form without ray florets is in all parts a little 

 greater. The ovary is 2 mm. long (instead of 1*5 mm. in the 

 first form), the corolla tube 4*5-5 mm. (instead of 4-4*5).' As 

 the receptacle is flat, while the capitulum is slightly conical, it is 

 obvious that the inner florets must be longer than the outer, and 

 in all the heads examined the florets of the discoid form have 

 been found, on the average, smaller than those of the rayed 

 flower. 



An abnormal disc floret was found in most of the heads, 

 occurring sometimes two or three times in a single head of the 

 intermediate form. This had two corollas, each with anthers 

 and style, arising from a single ovary. In some cases a second 

 ovary was indicated by a groove a short distance from one side, 

 in others two equal ovaries were united along their narrow 

 edge. 



In 1902, specimens of Aster tripolimn were gathered near 

 Barking (Essex) from an inland pool which was kept brackish 

 by the water which percolated through the river bank at high 

 tides. They were, fortunately, preserved as the largest flowers 

 which had come under my notice, some of the heads measuring 

 3 cms. in diameter. On examining them it was found that 

 though one head contained 35 ray + 48 disc florets, the others 

 had 17-24 rays and 23-36 discs, and were therefore inferior in 

 number of florets to many of the salt marsh flowers. The rays, 

 however, were almost uniformly 12 mm. long and 2 mm. broad 

 after dr3nng, so that their exceptionally handsome appearance 

 was due to an increase in the size of the rays instead of an 

 increase in their number. 



Bees and flies visit both formis alike. Caution must be 

 exercised in drawing conclusions from the number of insects 

 seen on a given area at any one time ; in a strong breeze very 

 few insects will be found on the exposed salt marsh, while at 

 the same time they may be abundant on the plants in the 



1905 February i. 



