The President's Address. By Lord Avebury. 299 



rugose, very dark reddish -brown by transmitted light, crustaceous 

 and brittle. 



They are mixed indiscriminately on the panicle. The large 

 brown ones germinate much more quickly than the small black 

 ones, which would seem, under natural conditions, to be more 

 adapted to remain in a resting condition in the ground during the 

 winter and germinate in spring. If such is the case they would 

 enable the plant to exist in a colder climate than the large ones 

 would. The plant occurs in Britain as a garden escape. 



Some fruits inclosed in the dry wing-like perianth were 

 dropped in a tumbler of water, and all of them floated for seven 

 days. At that time, contrary to what might have been expected, 

 the larger fruits containing the larger-sized seeds with the thin 

 grey testa and covered by the broad perianth segments had sunk, 

 and the seeds had commenced to germinate. At the end of 

 twenty-one days many of the seedlings had risen above the water, 

 and the cotyledons, already green, had commenced to expand. 

 The small black seeds with the crustaceous testa, covered by a 

 small perianth, were still floating after twenty-one days, and on 

 examination proved to be quite fresh and sound. 



A. hastata also has two forms of fruit. 



POLYGONACE.E. — Fruit a berry, utricle, or nut. In our English 

 species the fruit is a small, seed-like nut, inclosed in the persistent 

 flower, and containing one seed. The prevailing form is trigonous. 

 There are three styles, indicating the presence of three carpels. 



The persistent perianth leaves evidently serve as wings. 



The sepals of the Docks {Ilumex) have one or more, often red, 

 glands. These perhaps induce birds to carry them off, thinking 

 they may be sweet and good to eat. The persistent sepals no doubt 

 lighten the fruits, and in some species are deeply toothed or 

 laciniate, which would help to entangle them in the fur of animals. 



In Polygonum Hydropiper the nutlets are of two forms, 

 triquetrous or biconvex. The latter are much the more numerous. 

 In P. Persicaria also there are two forms (plate IV. figs. 10a, 10b, 

 10c, lOd). 



In P. viviparum, a high Alpine form, more than one-half of the 

 flowers on the lower part of the stem are replaced by small bulbils 

 or enlarged buds that fall away and reproduce the plant. At high 

 elevations the growing season is often so short and the conditions 

 so adverse that the plant is unable to produce and mature seeds 

 before the return of winter. The flowers on the upper portion 

 of the stem seldom ripen seeds, but fall away some time after 

 flowering. 



This Polygonum may be compared with Sasrifraga ccrnua, which 

 produces numerous clusters of bulbils along the stem, and usually 

 only one flower on the top. S. stellaris and S. nivalis sometimes 

 behave in the same way. Akin to the above are the viviparous 

 forms of Poa alpina and Pestuca ovina. 



