768 



THE NATURE BOOK 



of independent movement, thej^ do not 

 form silicioiis skeletons, and tlicy are 

 peculiar to fresh water, wiiile Diatoms 

 abound in both fresh and salt water. 

 Desmids \-ary considerably in shape and 

 size, and are nearly all very beautiful 

 and graceful of form, one quite common 

 species resembling a tiny green new 



OK SPIROGYRA IN PROCESS OF 

 CONJUGATION. 



moon. A very handsome Desmid fre- 

 quently to be met with in ponds and 

 sluggish streams, is rather like a rosette 

 in shape. 



A very remarkable and interesting 

 plant which should be collected from the 

 pond in the spring of the 3'ear is the 

 Sj)irogyra. It appears on the surface of 

 the pond as small collections of very fine, 

 almost hair-like stems, more or less 

 tangled together. Under suitable con- 

 ditions, it is possible to witness the whole 

 process of reproduction in this plant, 

 which is effected by a process called con- 

 jugation, and is very interesting. If 

 some of the tangle of Spirogyra be 

 placed in a shallow glass pan of water, 

 the stems, if about to conjugate, will, with 

 tlie aid of a magnifying glass, be seen 

 gradually to straighten out and draw 

 towards one another. As the stems draw 



together, the cell walls down the side 

 nearest to the approaching stem will in 

 each case begin to swell outwards until 

 at last they meet and join, giving the 

 two stems the appearance of a miniature 

 ladder. While the cell walls have been 

 growing, the contents of each cell ha\e 

 been passing through a series of changes, 

 until the whole protoplasmic con- 

 tents has gathered towards the 

 nucleus. When the two opposite 

 cell walls ha\'e grown out and 

 united, the nuclei of the two 

 cells either both meet and join 

 in the passage formed by the 

 union of the two cell walls, or 

 one of the nuclei passes through 

 the passage into the opposite 

 cell, where it comes into contact 

 and fuses with the nucleus of 

 that cell. As a result of the 

 fusion of the two nuclei, growth 

 takes place around them, and 

 an o\'al resting spore is formed, 

 the chains or ladders break up, 

 and the spores sink to the bot- 

 tom of the pond, where, after 

 a certain period of rest, they 

 start into active growth, each 

 spore becoming the originator of one of 

 the slender Spirogyra stems. 



In the foregoing articles I have en- 

 deavoured to give some account of a few 

 of the wonders and curiosities of j)ond 

 life, but it would require more than a 

 dozen volumes of The Nature Book to 

 do anything like justice to the teeming 

 animal and vegetable life of the pond. 

 Every pond will be found to have its own 

 characteristic forms of life, for variation of 

 locality, vegetation, and water supply, are 

 determining factors as regards the number 

 and species of creatures and plants to be 

 found in each pond. While some forms of 

 life are present in every pond, others are 

 extraordinarily local, but during most 

 months of the year the lover of Nature 

 will find some object of interest in the 

 wayside pool, some beautiful or curious 

 representative of ]iond life. 



P". Maktix DrxcAX. 



