1883.] 



MICROSCOPICAL JOURNAL. 



23 



veloped with a sheath, as shown in 

 fig. 6, e. 



Itzigsohn, more than twenty-five 

 years ago, found that Hcipalosiphon 

 Braunii, a phmt allied to Sirosip/ion, 

 (fig. 6,y), also developed from a AWAv, 

 or a Microcystis. 



It will be seen, therefore, that the 

 study of the unicellular forms should 

 first be directed to solving the question 

 of their origin or future growth. When 

 we consider that the swarm-spores, 

 when once they pass into the stage of 

 unicellular, vegetative growth, or multi- 

 plication, may give rise to many genera- 

 tions of new cells before resuming the 

 parent form, the tedious nature of 

 such investigations must be self-evi- 

 dent. But, more than this, even these 

 unicellular forms vary in appearance 

 under different conditions of moisture, 

 and give rise to a polymorphism 

 which may be exceedingly confusing. 

 It is often utterly impossible to dis- 

 tinguish between the swarm-spores of 

 very different plants, except by fol- 

 lowing their life-history. Separate 

 the gonidia of a lichen, and compare 

 it with some, spores of alg£e, and it is 

 impossible to distinguish them apart. 

 What, then, shall be our generic or 

 specific characteristics for the alg£e, 

 if we cannot even tell an alga from 

 the gonidia of a lichen ? 



It would be useless to attempt to 

 answer this question in the present 

 state of our knowledge. The evidence 

 seems indisputable that many of the 

 forms now classed as unicellular algaj 

 are but the propagating spores of 

 higher algae. However, it does not 

 follow that there are no algae which 

 attain their full development as single 

 cells. 



It has been thought by some that 

 there must be a process of conjuga- 

 tion sometime in the life-history of 

 every plant, to insure its contin- 

 ued existence. Conjugation is the 

 union of two elements which may 

 be distinguished as male and female. 

 Among these low plants, however, no 

 such distinction can be recognized, 

 and it may be fairly doubted if ii 



exists at all. It may be that the 

 two swarm-spores that unite, as be- 

 fore described, are no more different 

 than any two other protoplasmic cells, 

 and yet by their union they may serve 

 to perpetuate the species. It should 

 be remembered that in these lower 

 plants all the functions of life reside 

 within each single cell, and it seems 

 impossible that the differentiation of 

 special male and female elements or 

 cells, should be manifested so low in 

 the scale of life. 



Among the green-celled, gelatinous 

 algae it is a hopeless task to draw a 

 line even between the genera, to say 

 nothing of the species. We may say, 

 in general terms, that a gelatinous 

 layer containing green or brown, spher- 

 ical or oval cells irregularly scattered 

 through it, is a Pahnella; when the green 

 cells are arranged with some regularity 

 in groups of four, we have Tetraspora. 

 In typical forms this distinction is 

 clear enough, but in practice it will be 

 found that it is not easy to always tell 

 to which of these genera the plant be- 

 longs. So it is throughout all the 

 unicellular plants, — the species and 

 the genera run together. Take, for 

 instance, the two plants Glceocystis and 

 Glxocapsa. The latter is shown in fig. 

 6 c, the former only differs from Glceocys- 

 tis in the color of the chlorophyll, which 

 is of a brighter green. It is probable 

 that many of the lower algae that are 

 now regarded as belonging to dis- 

 tinct genera, will eventually be found 

 to be only different stages of develop- 

 ment of other algae, or in many cases, 

 modified forms of growth produced by 

 the conditions of life, such as the 

 greater or less abundance of water, 

 the rapidity of growth, etc. 



Such a supposition finds some sup- 

 port in the fact, well known to stu- 

 dents of the algae, that certain forms 

 will be found in a pulverulent condi- 

 tion in dry weather, while with abun- 

 dance of water a gelatinous investment 

 surrounds them. It follows that the 

 generic name of an alga will some- 

 times change with the habitat. Glce- 

 ocystis, for example, is found upon 



