350 THE SEA SHORE 



Some of the algae may be reproduced without the agency of any 

 sexual elements ; that is, without the aid of parts that correspond 

 with the ovules and the fertilising pollen of a flowering plant. 

 Some of these are reproduced by a repeated subdivision, or by the 

 separation of a portion of the plant that is capable of independent 

 growth ; while others produce spores that do not result from the 

 fusion of two different cells. In most, however, sexual differences 

 are to be observed, some cells being modified into female organs, 

 containing one or two more minute bodies that are capable of 

 developing into new plants after they have been fertilised, and 

 other cells produce the male elements by means of which the fertili- 

 sation is accomplished. The fertilised cells are spores, but are 

 named differently according to the nature of their development. 

 They all differ from true seeds in that they never contain an embryo 

 plant, but germinate by the elongation of some particular part, 

 which subsequently grows by a continuous process of cell-division ; 

 or the cell-division may originate directly in the spore without any 

 previous elongation or expansion. 



The sea weeds are usually classified according to the colour of 

 their spores ; but, since this colour generally corresponds with that 

 of the plant itself, we may almost say that they are grouped accord- 

 ing to their general tints. There are three main divisions : 



The Chlorospermecs, or Green-spored ; 

 The Rhodospermece, or Red-spored ; and 

 The Melanospermea, or Brown-spored. 



The ChlorospermetB contain no colouring matter other than the 

 chlorophyll. They are mostly small weeds, of a delicate green 

 colour ; and, although they are not particularly conspicuous on our 

 shores, they contribute very considerably to the beauty of the rock 

 pools, where their delicate green fronds contrast richly with the 

 olive Melanosperms and the pink and white corallines. The thallus 

 or plant-body is very varied in form, sometimes consisting of a 

 broad membrane, but more commonly of tufts of slender green 

 filaments or of narrow, flattened fronds. 



These weeds are most beautiful objects for the microscope, and 

 they are generally so thin and transparent that no section-cutting 

 is necessary, nothing being required except to mount very small 

 portions in a drop of water. In this simple manner we may study 

 the beautiful arrangement and the various forms of the cells of 

 which they are composed. The more delicate species will be found 



