250 



HINTS AND NOTES 



during the summer months, and the winter is, 

 as in the case of most other plants, a period of 

 rest. The vejjetative cycle is broken in winter 

 by the elaboration of such special structures. 

 Many plants simpl)' sink to the bottom, and in 

 the sprinsiT rise ag^ain to the surface. The 

 hibernacula drop olT and sink to the bottom 

 till the spring. 



Water Lilies die down to the rhizome. Only 

 a small percentage of aquatics are annual or 

 biennial, as Duckweed, Horned Pondweed and 

 .Awl-wort. 



The Pollination of Aquatic Plants. — The 

 aquatic habitat of water plants affects all the 

 phases of their life history. This applies not 

 only to their vegetative organs, but also to the 

 reproductive processes, or devices for the con- 

 tinuity of the species. 



Some i'fw aquatic plants hardly raise their 

 flowers above water, or not at all as in the 

 case of Zostera, and in I'allisiicria, a sub-tropi- 

 cal plant which has been found in the Canal 

 at Manchester. The rest are more or less 

 normal, the reproductive parts of aquatic plants 

 being less altered than their vegetative portions. 

 But there are some features in which they 

 differ from land plants. Thus a number of 

 them have very small (reduced) flowers, and 

 few are sweet-scented. A large proportion 

 have white or yellow flowers. The plants in 

 the reed-swamp association are the most 

 diverse, and most closely allied to land plants. 



Beetles help to pollinate the White Water 

 Lily, and many are pollinated b)' small flies, 

 as Water Plantain. Whilst cross-pollination 

 is effected by insect agency in the majority of 

 cases, a number are more liable to be self-pol- 

 linated, as Great Yellow Cress, Great Water 

 Stitch wort, Three -lobed Butterbur, Yellow 

 Loosestrife, &c. Heterostylism is found in 

 Purple Loosestrife and Yellow Loosestrife, 

 which are trimorphic. In Great Hairy Willow 

 Herb and Creeping Jenny the anthers and 

 stigma are ripe together. The Marsh Bed- 

 straw, Great Water Stitchwort, Brooklime, 

 .Amphibious Knotgrass, Flowering Rush, ripen 

 their anthers first, before the stigma. Butter- 

 bur, Frogbit, and Reed ^L'lce are dioecious. 

 Coltsfoot, Bur Reed, Bulrush, and the Reed 

 m.-iture their stigma first. Duckweed and 

 .Arrowhead are monoecious, and the former is 

 pollinated by aquatic insects. The following 

 are wind -pollinated: Crack Willow (visited 

 also by bees), Reed Mace, Frogbit, Bur Reed, 

 Sweet Flag, Bulrush, Wood Club Rush, and 

 the Reed. 



The Dispersal of Seeds in Aquatic Plants. — 

 The aquatic character of the habitat introduces 

 new features into the mode of dispersal of the 

 seeds. The seeds of submerged and floating 



plants must in these cases germinate in the 

 mud at the bottom. Heavy seeds are more 

 likely to be deposited not far from the plant, 

 sinking to the bottom. But in soine the seed- 

 coat contains air vessels and the fruit or seeds 

 float along, some even germinating at the 

 surface of the water. In this case wind and 

 water currents enter into their mode of dis- 

 persal. Seeds of half-submerged plants in the 

 reed swamp, which may fall into the water, 

 are of this type, and one may note sometimes 

 a scum of small seeds that liave been drifted 

 together by capillary attraction, and driven to 

 the margin to germinate in the mud on the 

 banks. The Water Lily seeds are surrounded 

 by a spong)' aril with air spaces, and at first 

 float up to the surface. .Afterwards, when the 

 aril has rotted, the seeds fall again to the 

 bottom. 



The fruits or seeds of the following are dis- 

 persed by special agencies of the plants them- 

 selves: Meadow Rue, W'ater Cress, Great 

 Yellow Cress, Great Water Stitchwort, Purple 

 Loosestrife, Marsh B<'dstr;r\v, Water Belony, 

 Musk, .Mints, Gipsywort, Skullcap, Frilillary, 

 Wood Club Rush. Water Fennel, White and 

 Yellow Water Lily, Brooklime, .Amphibious 

 Knotgrass, Bur Reed, Sweet Flag, Duckweed, 

 Water Plantain, Arrowhead, Flowering Rush, 

 Bulrush, are chiefly dispersed by aquatic 

 agency, in some cases also by the wind. The 

 wind assists Great Hairy Willow Herb, Hemp 

 Agrimony, Fleabane, Three-lobed Butterbur 

 (also, owing to its hooked fruits, dispersed by 

 animals). Coltsfoot, Butterbur, Water Rag- 

 wort, Marsh Thistle; also A"ellow Loosestrife, 

 Creeping Jenny, Crack Willow, Frogbit, Yel- 

 low Flag, Reed Mace, and the Reed. Water 

 Fennel, Scorpion Grass, Bur Reed, may be 

 largely dispersed l>y animals. 



The Soil Equivalents of the Aquatic Habitat. 

 — Though true aquatics, especially free float- 

 ing t)"pes, are independent of soil, they, like 

 the submerged and floating types which are 

 anchored in mud or sand or gravel, &c., are 

 to some extent influenced by the character of 

 the substratum. 



Since the soil brought down by rivers and 

 . streams is of a particular character, it is natural 

 that plants that live in the reed swamp, or 

 upon the banks or low-lying ground, should 

 be dispersed elsewhere where the conditions 

 are similar. 



.At the same time there is a considerable 

 amount of peat or humus formed along a river 

 margin, which is usually black and amorphous, 

 and this is another requirement of such plants. 

 Others are addicted to a clay soil. Meadow 

 Rue, Water Cress, Great Water Stitchwort, 

 Purple Loosestrife, Great Hairy Willow Herb, 



