x 



;>d. By the differentiated contents of a xiii<//<> frustule prodnc 

 ing one sporangium, the most common mode of propagation a> 

 well as the lowest in the scale, as in the free form. <'i/ml><-/l<i 

 cusrpidata. 



Besides reproduction by conjugation there is multiplication 

 by division, and as diatoms do not grow these divisions tend to 

 make the resultant diatoms smaller ami smaller until some 

 become so minute as in the Nit:schi<i, _X<tri<-nhr and Am^lionr, 

 that while living they can go through the pores of filtering 

 paper ; a single frustule by constant division and subdivision of 

 its progeny, would give rise in twenty-five repetitions of this 

 process, to more than thirty million individuals, did they all 

 survive. 



As regards the longevity of diatoms, it maybe said that dried 

 specimens can not be revived, but they have been known to sur- 

 vive nearly a quarter of a century in their natural element 

 even though kept for long periods in the dark, and at times 

 frozen in solid ice. Their silicious covering is almost indestruc- 

 tible, resisting the strongest acids and passing unscathed through 

 very high degrees of heat. 



There are very few microscopic objects of more interest than 

 the Diatom or which return more ample rewards to the patient, 

 enthusiastic student. 



