THE DISTRIBUTION OF SPECIES BY OFFSHOOTS. 



and the whole shoot-apex, separated from the lower part of the stem, which has 

 long been in a leafless condition, is carried away by the currents of the water. 

 How far and for how long the shoot is carried about depends upon the local con- 

 dition of the sea-shore. Sooner or later its career of wanderer is arrested by the 

 trailing comb-like scales assuming the role of anchors. As soon as the anchor is 

 fast, some 2-4 roots develop from the lower internodes of the shoot; these pass 

 between the teeth of the comb-like anchor, and grow down into the muddy sub- 

 stratum, thus fixing the offshoot. All this happens at the end of winter. During 

 the following summer, the shoot, which is about 8 cm. long, and is anchored and 

 rooted in the mud, again grows up into a stem about a metre high, and next winter 

 its top again falls off just in the same way. It has already been mentioned (p. 457) 

 that this strange sea-plant very rarely blossoms or fructifies a circumstance which 

 confirms the supposition that the boundless colonies of it round the coasts of 

 Tasmania owe their origin to the offshoots distributed by the sea currents. 



The distribution of offshots by sea-water is a much simpler affair in the Sea- 

 wracks, Ulvas, and Florideae than in these other water-plants. When the sea is 

 stirred to its depths by violent storms and the spring-tide is higher than usual 

 the retreating waves leave any quantity of fragments of these plants behind 

 them. These have been torn by the raging water from the firmly -fastened 

 ribbons, nets, and threads below, and are then carried away by the billows. The 

 water drives them into clefts of the rocky coast or imbeds them in the sand and 

 mud of the shore, and, wonderful to relate, not a few of them flourish again, granted 

 of course that they are not speedily removed by subsequent tides and that the 

 circumstances are otherwise favourable. 



Much the same kind of thing happens on the banks of rivers and streams. A 

 portion of the plant -fragments brought by floods and stranded on the mud of 

 calm inlets undergoes decomposition. A larger portion remains fresh and living, 

 sending out roots and vigorous shoots. In the bed of the Danube, in addition to the 

 abundant creeping shoots of the Reeds (Phragmites) and various Sedges, Bul- 

 rushes (Scirpus, Typha), broken twigs of Salix fragilis, bits of roots of the Sea 

 Buckthorn (Hippophae rhamnoides), fragments of the rhizomes of (Enanthe Phel- 

 landrium and Acorus Calamus, leafy twigs and stolons of various species of 

 Pondweed, Water-Milfoil, and Water Ranunculus (Potamogeton, Myriophyllum, 

 Ranunculus aquatilis) are all distributed in this way. Sometimes these growths 

 settle in places where formerly no specimen of the kind had been seen for miles, 

 and the fact may be easily confirmed that the distribution of their offshoots is 

 actually brought about by flowing water in a very short time to great distances 

 and in great abundance. 



The distribution of offshoots in little brooks which flow down between Reeds 



and Rushes with a moderate fall, and scarcely ever overflow their banks takes 



aore quietly. A rapid flow occurs only in the middle of the channel, but 



the bank, and especially in the small inlets, the water is almost as still and 



m a closed-in lake, Here in these quiet spots are also to be found floating 



