XVI INTRODUCTION. 



sporangia of the species with which they were associated, and 

 indicated the several stages of the reproductive process. 



In another gathering containing Sgnedra radians, W. Sm., 

 collected by Christopher Johnson, Esq., at Hamson, Lancashire, 

 October 1851, the cysts containing "broods" of frustules evi- 

 dently belonging to the accompanying species were of frequent 

 occurrence. The progress of development was not so fully 

 traced as in the case of Cocconema Cist/da, as there were not 

 any examples in the Hamson gathering of the conjugated state 

 of the Synedra, but the appearance of the cysts and their contents 

 was equally characteristic with the former of the reproductive 

 process; and on a subsequent occasion, and at a distant locality, 

 I had the pleasure of detecting similar phaenomena in connexion 

 with the same species, leaving no doubt on my mind that the 

 cystoid condition is one stage in the normal method of its repro- 

 duction. Figures representing this state of Synedra radians, as 

 collected by myself in the neighbourhood of Lewes, in the 

 county of Sussex, November 1853, are given in Plate B. 89. 



On the whole, the facts at present within our knowledge seem 

 folly to warrant the conclusions that the conjugated state of the 

 Diatomaceae is the first step in the reproductive process of 

 these organisms, and that the sporangial products of this con- 

 dition become the parents of numerous young frustules destined 

 to renew the cycle of phaenomena which accompanies the life 

 and growth of the species from which the sporangia have them- 

 selves originated. 



That frequent, and apparently accidental or abnormal modi- 

 fications in the reproductive process should characterize its 

 progress in the Diatomaceae, will not surprise those who are 

 intimately acquainted with the lower tribes of plants. The 

 character of the structure and organization which distinguishes 

 such organisms involves but little specialization of function, and 

 admits an amount of disturbance and seeming irregularity that 

 would be altogether inconsistent with the more complex struc- 

 ture and specialized functions of the higher plant. There is 

 nothing, however, in the history of the reproductive process 

 among the Diatomaceae inconsistent with the ascertained laws 

 which regulate the growth of unicellular plants, or which 



