The President's Address. By Lord Accbury. 141 



means of small ovoid bulbs or bulb-like structures, which detach 

 themselves from the parent plant, and no doubt are carried about 

 by the water or by animals. 



Though we have only two native species, a third representative 

 of the order, Elodea canadensis — a native, as its name denotes, of 

 North America — is now firmly established in our waters. It appeared 

 in Ireland in 1836 and in Great Britain a few years later, and 

 spread rapidly. The plants are dicecious, and the male, which is 

 rare in America, has not yet been observed here, except near 

 Edinburgh. 



The plant is very brittle, which materially assists in its 

 dispersal. 



Stratiotes. — The male flowers of Stratiotes have about twelve 

 fertile stamens, and fifteen to thirty others which serve as honey- 

 glands. The female flowers have similar honey-glands. It is said 

 that in Northern Europe no male flowers have been observed, while 

 in Holstein they are not infrequent. The increase is with us mainly 

 by offshoots. During the winter the plant remains at the bottom 

 of the water. In spring it rises to the surface, producing fresh 

 leaves, flowers, and floating roots. After flowering it again sinks, 

 so that the seeds ripen in safety. Young plants are also pro- 

 duced at the end of long stalks which spring from between the 

 leaves. Towards the end of August the plant rises a second 

 time, and is at first surrounded by the young ones. The connect- 

 ing stalks then die and decay, thus setting them free. Finally, 

 they descend to the bottom for the winter. 



Oechidace.e. — We have in Britain sixteen or seventeen genera 

 and about forty-four species. The ovary is inferior, 1-celled, with 

 three parietal placentas, though there are a few species of Cypri- 

 pedium, in which the ovary is perfectly 3-celled. 



The testa is loose and reticulate, in a few cases flattened out 

 into a wing. These, and indeed all the seeds, are no doubt dis- 

 persed by the wind. They would, moreover, of course readily 

 adhere to any passing animal. 



The capsule is 3-valved, with innumerable minute more or 

 less fusiform seeds (fig. 23). It has been estimated that a capsule 



Fig. 23. — Seed of Orchis maculata. x 40. 



of Cattleya contains more than 1,000,000, and the seed of G-oodyrra 

 repens is said to weigh only 0*000002 of a gram. 



In some tropical Orchids, as, for instance, in Vanda, the fruits 

 ■contain, besides the small seeds, hair-like cells with oblicpiely pitted 

 walls. These are very hygroscopic, and twist about if the con- 

 ditions of the air vary, thus carrying the seeds from the interior to 



