b W. B. TURNER, FRESII-WATER AI/LE OF EAST INDIA. 



which tlie limits attainable by specific divergence, as occurring in these organisms, could 

 more easily and satisfactorily be determined.» Beng. Desm. p. 184. 



(b) »It is almost impossible to arrive at a correct estimate of the outburst of fresh 

 life to which microscopic forms are subject in such a elimate, by any comparison with 

 what is observable elsewhere. Immediately prior to the setting-in of the annual rains, 

 the pools, swamps, water-courses, and even the majestic rivers, are well nigh dried up. 

 The surface of the soil is parched into a layer of impalpable dust, and the remnants of 

 all the minute tribes of plants are carried to and fro, by the slightest winds, amongst the 

 dusty particles to which they themselves largely contribute. At this period the sporangial 

 state is assumed both by the Desmidiacete and Diatoruacese, and it may be regarded, there- 

 fore, as a species of hybernation, during which vitality is maintained under the minimum 

 of the conditions (c) essential to its continuance, and without the interposition of which 

 phase these organisms would become extinct. For upwards of two months the rains con- 

 tinue to fall incessantly. The whole country is flooded, and the rivers expand to the 

 proportions of inland seas. It is useless, as yet, to search for the Desmidiacese. Xo 

 sooner, however, have the rains and inundations subsided, than the mud-laden pools clear 

 down, the magic influences of light and heat are permitted to operate, and in an in- 

 credibly brief period the surface, the bottom, and the body of the waters absolutely teem 

 with the crowded masses of animal and vegetable life.» Beng. Desm. p. 185. 



Concerning the first quotation (a), I would remark that for Dr. Wallichs view 

 there is much to be said, and in proof of his view I have myself observed considerable 

 divergence in some forms (e. g. Micrasterias Cruas-melitensis), but space did not pennit 

 of my hguring many, or entering into full detail concerning them. On the other hand 

 many forms are absolutely identical with well known European ones, as the hgures of 

 Wallich and myself prove. The subject is very debateable (Cfr Archer in Dub. Micr. 

 Club. Träns. 1865, and Wallich' s letter to him on »variation»); still it must be admitted 

 that Nature is so prolitic in design that no two leaves upon a tree, no two Desmids, are 

 exactly alike! If it be argued that, because we cannot absolutely see the effects of evolu- 

 tion, which is is ever-changing and unceasing, such effects are not existent, it is merely 

 a, faqon de parler and no argument at all — and I cannot help but agree for the must 

 part with Wallich (in litt. ad Archer 1. c), »the law which it is assumed governs the 

 limits of species is no law, but only a conditional direction, holding good only so long 

 as the surrounding conditions continue the same», i. e. through the environment being 

 the same through a lengthened period of time. 



Upon the second paragraph I would observc (c) that the lower orders of planta seeni 

 endowed with peculiar properties of vitality and continuance under stress of elimate, and 

 Wallichs remarks are continued, under the opposite extreme, in "The Desmidiea' of Green- 

 land' (Träns. Roy. Mic. Sci. p. 130, 1869,) the locality cited, Godhaab, being 64° N. Lat., 

 and the pools frozen up for 8 months in the year. It is also significant that various 

 Siberian forms observed by Boldt have been found in Japan by Roy and Bisset, and by 

 myself in the Indian material. The remarks of Dr. NoRDSTEDT in Fr. Alg. X. Z. j). 5, 

 1888, are exceedingly interesting, as bearing upon the influence of region with reference 

 to the lower Alg». 



