HARD WICKE >S SCIENCE - G OSSIP. 



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results as we might desire, and the greatest circum- 

 spection is necessary in the interpretation of the facts 

 observed. That which we appear to know for certain 

 is that conjugation takes place in diatoms, and that 

 the material result of this is the formation of what is 

 called a sporangium. This proceeds either from the 

 condensation of the protoplasm and endochrome con- 

 tained in the interior of a single frustule, of which the 

 valves are separated in such a manner as to enlarge 

 the internal capacity of the frustule, the matter thus 

 amassed giving place, according to the species, to the 

 formation of one or two bodies, more or less round or 

 oval ; these very soon secrete on their surfaces a hard 

 shell (test-resistant). These are the Sporangia, or 

 the intimate union and fusion of the protoplasm of 

 two contiguous frustules that have partially opened 

 along the sections of the connectives for its liberation. 

 Here also is formed, according to circumstances, one 

 or two sporangia. When the sporangium [is pro- 

 duced by a single primitive frustule, it is probable that 

 the original primordial utricle, which was already pre- 

 viously divided into two for the purpose of deduplica- 

 tion before the secretion of the new siliceous valves, 

 and that the sporangium, formed of the differentiated 

 protoplasm, produces that of the two young utricles. 

 This, however, requires to be verified by direct obser- 

 vation. In both cases there is promptly developed in 

 the interior of the sporangium a special body, which 

 varies in form according to the genus, which grows 

 rapidly, and which possesses an envelope rich in 

 silica, and is able to resist calcination and the 

 action of concentrated acids ; it is often wrinkled 

 across the external surface ; this is the Aitxospore. 

 This last is the analogue of the zygospore of Zygne- 

 maceae. Its growth at last bursts the sporangium, 

 and carries with it to its apices, the two halves of the 

 sporangium-like little caps. 



"When the auxospore has attained a size generally 

 double, or even more, of the frustule that has origi- 

 nally produced it, we discover in its interior, lying 

 across the envelope, the valves forming the new frus- 

 tule. These last are apparently the product of a true 

 generative act, and which we are justified in consider- 

 ing for the moment as sexual, although our means of 

 observation up to the present are much too imperfect 

 to permit of our being able to distinguish the male 

 from the female element in the products of conjuga- 

 tion. The first frustule is called the sporangia! frus- 

 tule. With this is destined to commence a new cycle 

 of vegetative generations by deduplication, which 

 continues up to the moment that a new conjugation 

 takes place. It restores also the normal size of the 

 frustules degenerated by the repeated deduplications, 

 and we see here the singular phenomenon of the child 

 being at its birth much larger than its parents. The 

 sporangial frustule is always enormously large in com- 

 parison with its parents, the empty valves and con- 

 nectives of which are generally retained by a mass of 

 gelatinous matter secreted previous to the act of con- 



jugation. We believe that other modes of reproduc- 

 tion exist in the diatomacea? beside that of conjuga- 

 tion, but the biology of these little beings is much too 

 imperfect to enable us to hazard any profound hypo- 

 thesis on this subject. It is evident that all the 

 frustules do not finish by conjugating ; this is highly 

 improbable, when we consider the rarity of that 

 phenomenon. Some other explanation is necessary 

 to account for the variations in the dimensions we 

 meet with in the different individuals of the same 

 series other than that of deduplication, as without it 

 those frustules that escape conjugation would go on 

 diminishing in size indefinitely, and we know from 

 observation that every species of diatom possesses a 

 maximum and minimum of dimension which it never 

 passes.* 



The rapid appearance of species where they did not 

 previously exist — their periodic succession at deter- 

 mined seasons, and which we had never been able to 

 find in the intervals in the same locality — this presents 

 the possibility of a mode of generation which is only 

 yet suspected, by germs, by micro or macro-zoospores, 

 possibly even in the first case with the formation of 

 zygozoospores, as it takes place among many of the 

 inferior algae who live under the same conditions as 

 the diatoms. 



We enter here a field of study of the greatest interest 

 and novelty to every naturalist furnished with a good 

 microscope, and possessing time and patience neces- 

 sary for such researches, and we dare affirm that any 

 member of a microscopical society who shall follow 

 with care the entire life cycle of a single species of 

 diatom, even the commonest, will probably render a 

 greater service to science than if he had described and 

 figured hundreds of frustules from the four quarters of 

 the globe. 



Note. — In a communicationf to M. Deby, Professor 

 H. L. Smith makes the following remarks : — 



' ' I have received your brochure, entitled, ' Ce que 

 c'est qu'une Diatomee,' for which I thank you. What 

 you say is generally correct. I have myself published 

 a part in the 'Lens' in 1873, but I entirely differ 

 from you on certain points. The communication 

 which you say exists between the internal protoplasmic 

 substance and the external medium does not take 

 place, as you say, along the sutures of the connective, 

 but in the naviculus, properly so called ; it exists along 

 the raphe or median line, and in the Nitzschias and 

 Surirellas along the ala? and carina?. (This is an in- 

 teresting confirmation of Ehrenberg's observations, 

 who had also studied this phenomenon many years 

 before J. D. ) I possess drawings showing the injec- 



* The process of self-division, no doubt, gradually exhausts 

 the vigour of the sporangial frustule, but this power is possibly 

 retained longer by some individuals than others (thus bearing 

 a striking resemblance to parthenogenesis in the Aphides, &c), 

 but there is probably no fixed limit. I have seen much smaller 

 valves of A ulacodiscus Kittoni in a New Zealand gathering 

 than in a copious and pure gathering from Vera Cruz. — F. K. 



t A translation into the French appears in the Bulletin de la 

 Socicte Beige de microscopie for Dec, 1S77. 



