608 iS^^ Jo^''^ Luhhoch [Feb. 18, 



provided with a red " eye-spot" as it has been called, which, at any 

 rate, seems so far to deserve the name that it appears to be sensitive to 

 light. This mode of progression is, however, only suitable to water- 

 plants. One group of small, low-organised plants, Marchantla, develop 

 among the spores a number of cells with spirally thickened walls, 

 which, by their contractility, are supposed to disseminate the spores. 

 In the common Horse Tails (Equisetum), again, the spores are pro- 

 vided with curious filaments, terminating in expansions, and known 

 as " elaters." They move with great vigour, and probably serve the 

 same purpose. 



In much more numerous cases, seeds are carried by the wind. 

 For this of course it is desirable that they should be light. Some- 

 times this object is attained by the character of the tissues themselves, 

 sometimes by the presence of empty spaces. Thus, in Valerianella 

 auricula, the fruit contains three cells, each of which would naturally 

 be expected to contain a seed. One seed only, however, is developed, 

 but, as may be seen from the figure given in Mr. Bentham's excellent 

 ' Handbook of the British Flora,' the two cells which contain no seed 

 actually become larger than the one which alone might, at first sight, 

 seem to be normally developed. We may be sure from this that they 

 must be of some use, and, from their lightness, they probably enable 

 the wind to carry the seed to a greater distance than would otherwise 

 be the case. 



In other instances the plants themselves, or parts of them, are 

 rolled along the ground by the wind. An example of this is afforded, 

 for instance, by a kind of grass {Spinifex squarrosus), in which the 

 mass of inflorescence, forming a large round head, is thus driven for 

 miles over the dry sands of Australia until it comes to a damp place, 

 when it expands and soon strikes root. 



In Pumilio argyrolepis, an Australian Composite, the pappus, or 

 portion corresponding to the feathered crown of the Dandelion seed, 

 consists, as described by Mr. Darwin,* of nine scales (or sepals), 

 expanded like a flower ; the lower part of the fruit, which encloses the 

 true seed, is bent nearly at a right angle, and in form closely resembles 

 a human foot. The upper side or instep is smooth, but the toe and 

 sole, which are about gV i^^^ i^ length, are covered with from 30 to 40 

 little bladders, each formed of a thin skin and containing a small 

 lump of gum. When the fruits are moistened these bladders burst 

 and the gum exudes. As long then as the fruits remain dry, they are 

 easily blown about by the wind ; but as soon as they alight on a damp 

 spot, the gum exudes and glues them to the ground. If a pinch of 

 these seeds be dropped on a piece of paper, the greater number fall 

 upright like shuttlecocks, but even if they alight on one side the 

 tendency of the gum is to pull them upright, so that they look as if 

 each had been placed upright and carefully gummed. It is not clear 

 whether this position is of importance to the germination of the seed. 



♦ ' Gardeners' Chronicle,' 5th Jan. 1881, p. 4. 



