The President's Address. By Lord Avebury. 



153 



for some time ; in many cases, also, this is promoted by the presence 

 of air-chambers in the cortical parenchyma. Under these circum- 

 stances, they must often be carried about by birds. 



The seeds of Alisma are campylotropous, and ribbed longitudi- 

 nally with short transverse ridges. I have described the germina- 

 tion in my book on Seedlings. The hypocotyl (fig. 29) is peculiarly 

 thickened. It produces numerous root-hairs from the edge of the 

 thickened extremity. These serve to fix it in the soil or mud. The 

 radicle does not begin to grow for five or six days, and is at first 

 devoid of root-hairs, which, however, after that are copiously 

 developed. The cotyledon is long, linear, or filiform, and at the 

 base sheaths the plumule. 



In Triglocliin palustre (fig. 29) the fruits are sharply pointed, 

 diverging, and turning downwards, being 

 attached by their summits to a stiff erect 

 axis, so that they are easily brushed off 

 by, and run into the fur or skin of, any 

 passing animal. 



The seed conforms to the capsule. The 

 elongation of the carpels may serve to 

 prevent them from sinking too deeply — 

 they recall the seeds of Narthecium in this 

 respect. 



The fruit of T. maritimum is oblong, 

 somewhat inflated, acutely 6 -ridged, cor- 

 responding to the six carpels, and with six 

 deep grooves, one on each carpel. 



Naiadace^;. — In this order the car- 

 pels are either two or four, each with one 

 ovule. The fruit consists of one, two, or 

 four nuts, generally each with one seed, 

 but sometimes with several. The fruit is 

 generally a nut, but sometimes a berry. 



There are sixteen genera and over 100 

 species ; in Britain the order is represented 

 by five genera and about fifteen species. 

 Some authorities, however, consider that Scheuchzeria and Tri- 

 glochin belong to this order, rather than to the AlismaceaB. 



In Potamogeton there are four carpels ; the embryo is curved 

 round the seed, which itself is horse-shoe shaped. The outer wall 

 of the fruit is somewhat fleshy, probably sometimes eaten by birds. 

 The plant is somewhat brittle, which no doubt aids in its dissemina- 

 tion. They much resemble the achenes of Ranuncidus, having a 

 more or less recurved beak. 



In Zannichellia the fruit consists of two to five free, radiating 

 carpels. Each is curved or slightly reniform, laterally compressed, 



Fig. 29. — Triglocliin palustre. 

 After Bentham. (Prom 

 Bentharn's Brit. Flora, 

 p. 800, fig. 963.) 



April 21st, 1909 



M 



