542 MICKOSCOPIC FORMS OF VEGETABLE LIFE THALLOPHYTES 



may sometimes be distinguished, and can always be brought into 

 view by tincture of iodine, which turns the * endochrome ' to a 

 brownish hue, and makes the nucleus (G) dark brown. Other cells 

 are seen (B), which are considerably elongated, some of them 

 beginning to present a sort of hour glass contraction across the 

 middle ; and when cells in this condition are treated with tincture 

 of iodine, the nucleus is seen to be undergoing the like elongation 

 and constriction (H). A more advanced state of the process of 

 subdivision is seen at C, in which the constriction has proceeded to the 

 extent of completely cutting off the two halves of the cell, as well as of 

 the nucleus (I), from each other, though they still remain in mutual 

 contact ; in a yet later stage they are found detached from each 

 other (D), though still included within the same gelatinous envelope. 

 Each new cell then begins to secrete its own gelatinous envelope, so 

 that by its intervention the two are usually soon separated from 

 each other (E). Sometimes, however, this is not the case, the 

 process of subdivision being quickly repeated before there is time for 

 the production of the gelatinous envelope, so that a series of cells 

 (F) hanging on one to another is produced. There appears to be no 

 definite limit to this kind of multiplication, and extensive areas 

 may be quickly covered, in circumstances favourable to the growth 

 of the plant, by the products of the binary subdivision of one 

 original cell. This, as already shown, is really an act of yrowth. 

 which continues indefinitely so long as moisture is abundant and 

 the temperature low r . But under the influence of heat and dryness 

 the process of cell- multiplication gives place to that of ' conjugation,' 

 in which two cells, apparently similar in all respects, fuse together 

 for the production of a * zygospore,' which (like the seed of a 

 flowering plant) can endure being reduced to a quiescent state for 

 an unlimited time, and may be so completely dried up as to seem 

 like a particle of dust, yet resumes its vegetative activity whenever 

 placed in the conditions favourable to it. The conjugating process 

 commences by the putting forth of protrusions from the boundaries 

 of two adjacent cells, which meet, fuse together (thereby showing 

 the want of firmness of their ' ectoplasms '), and form a connecting 

 bridge between their cavities (K). The fusion extends before long 

 through a large part of the contiguous sides of the two cells (L) ; 

 and at last becomes so complete that the combined mass (M) shows 

 no trace of its double origin. It soon forms for itself a firm cellulose 

 envelope, which bursts when the 'zygospore' is wetted; and the 

 contained cell begins life as a new generation, speedily multiplying, 

 like the former ones, by binary subdivision. It is curious to observe 

 that during this conjugating process a production of oil particles 

 takes place in the cells; these are at first small and distant, but 

 gradually become larger and approximate more closely to each other, 

 and at last coalesce so as to form oil-drops of various sizes, the green 

 granular matter disappearing ; and the colour of the conjugated 

 body changes, with the advance of this process, from green to a light 

 yellowish brown. When the zygospore begins to vegetate, on the 

 other hand, a converse change occurs; the oil-globules disappear, 

 and green granular matter takes their place. 



