Minnesota Plant Life. 513 



are generally provided with swimming lashes, or their vestiges, 

 though, sometimes, as in red algae, these are altogether lost 

 and the sperms depend upon water currents for their transfer 

 to the eggs. 



After a sperm and egg have fused by a complex process 

 entailing a profound rearrangement and combination of parts 

 the resultant cell, known as the fecundated egg, becomes capable 

 of elaborating a new organism. 



There are, then, in the plant world, four types of repro- 

 ductive cells: i, the originally perfect cell or spore; 2, the im- 

 perfect motile, male cell or sperm ; 3, the imperfect quiet, female 

 cell or egg, and 4, the secondarily perfect cell or fecundated egg. 

 The story of plant reproduction concerns the formation, struc- 

 ture and behavior of each of these four types of cell and the 

 interrelations that arise between them, their products and the 

 mature areas of the individual upon which they are produced. 



Production of spores. Almost all spores are of microscopic 

 size. In quantity, they appear as a dust. The spores of a 

 puff-ball or the pollen of an Easter lily will illustrate this. 

 There are two principal methods of spore production. They 

 may be formed either from superficial cells of the body, by 

 abstriction, or from the contents of special cells known as spore- 

 mother-cells. The former method is illustrated by the blue 

 moulds, mushrooms, red algae and related plants, in which cer- 

 tain superficial cells pinch off their free ends as one or more 

 special spore-cells. The latter method is much more universal, 

 and characterizes mosses, ferns and all higher plants. Further- 

 more, it is the method common in many types of algae, such 

 as the brown seaweeds, and in many fungi, such as the black 

 moulds, fish-moulds, and sac-fungi. Spore-mother-cells may 

 produce, in different types, from one to many hundreds of 

 spores. Large numbers arise in the mother-cells of the giant 

 kelp, the fish-moulds and the black moulds. In many sac- 

 fungi the number is commonly two, four or eight, while in liver- 

 worts, mosses, ferns and the higher plants four spores are ordi- 

 narily produced from each mother-cell, except in the instance 

 of embryo-sacs. 



Spore-producing areas are often aggregated as definite or- 

 gans. Examples of such are the gills of mushrooms, upon 



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