322 REPRODUCTION IN PLANTS 



tacts with a suitable object to which it becomes attaxihed 

 by the ciliated end. The cilia are then withdrawn and 

 thicker blunter protrusions of the cell body are extended 

 over the substratum. They seek out and make use of its 

 irregularities of form to secure a firm hold. The protru- 

 sions become covered with a cellulose wall at the same 

 time that the whole cell is forming its wall. When 

 attachment has been completed the cell begins to elongate 

 and presently divides. The two new cells remain joined 

 and make a little two-celled filament. A continuance of 

 cell division elongates the filament until it presently 

 reaches a degree of maturity when it will in its turn pro- 

 duce motile reproductive cells. On account of their 

 number and movement these are called swarm spores or 

 sometimes zoospores. 



(Edogonium (Fig. 81) is a somewhat more highly de- 

 veloped green alga than Ulothrix but will serve to illus- 

 trate the same phenomenon of reproduction by non- 

 sexual swarm spores. It too is attached at the base and 

 free at the apex. It grows by cell division. Occasionally 

 (or frequently if the conditions are just right) some of 

 its cells withdraw their protoplasm from contact with the 

 enclosing wall and round up. Each cell then produces 

 a single swarm spore. The old cell-wall breaks and the 

 swarm spore escapes and swims about vigorously by 

 means of a crown of cilia at the smaller end. It finally 

 settles down in the same way described for Ulothrix and 

 grows into a new filament. 



Essentials of Asexual Reproduction. — Though 

 there are a number of other different forms of non-sexual 

 reproduction among the lower plants, it is probable that 

 these illustrations will suffice to make clear its essential 

 features. All agree in that the reproductive cells — 

 whether they are just ordinary body cells or special swarm 

 spores — have arisen through ordinary cell division and 

 have identically the same kind of nuclei. Each and every 

 cell of these plants, whether ordinary vegetative or repro- 



