100 TENTH ANNUAL REPORT OF 



points ; these tubercles come into contact, and at length become con- 

 fluent ; the dissepiment between them vanishes, and a tube is thus 

 formed connecting the two cavities together. Through this tube the 

 matter contained in both the okl cells is transmitted and becomes 

 mixed ; changes take place in its organization, and at length a spo- 

 rangium, or new cell filled with spores is formed from it, either in 

 one of the old cells, or commonly at the point of the connecting tube, 

 where the two are soldered together. Then the old empty cells or 

 plants die, and the species is represented by its sporangium,^ which 

 may remain dormant, retaining vitality for a considerable time, as 

 from one year to another, or probably for several years. These spo- 

 rangia, which are abundantly formed -at the close of the season of 

 active growth, become buried in the mud at the bottoms of pools, 

 where they are encased on the drying up of the water in summer, and 

 are ready to develop into new fronds on the return of moisture in 

 spring. 



Many of the lower Algas form fruit in this manner, to which the 

 name conjugation is technically given. The thread-like Silk-weeds of 

 ponds and ditches {Zygnemata and llougeotice, &c.,) are good exam- 

 ples of such a mode of fruiting. In these almost every cell is fertile, 

 and when tw^o threads are yoked together, a series of sporangia will 

 be formed in one thread, while the other will be converted into a 

 string of dead, empty cells. Before conjugation there was, seeming- 

 ly, no difference between the contents of one set of cells and of the 

 other ; so that there is no clear proof of the existence of distinct 

 sexes in these plants, however much the process of fruiting observed 

 among them may indicate an approach to it. 



The process of fruiting in the higher Algfe appears to be very sim- 

 ilar : namely, spores or sporangia appear to be formed by certain cells 

 attracting to themselves the contents of adjacent cells; and in the 

 compound kinds, empty cells are almost always found in the neigh- 

 borhood of the fruit cells ; but with the complication of the parts of 

 the frond, the exact mode in which spores are formed becomes more 

 difiicult of observation. At length, among the highest Algfe we en- 

 counter what appear to be really two sexes, one analogous to the 

 anther, and the other to the pistil of flowering plants. It would 

 seem, however, that it is not each individual spore which is fertilized, 

 as is the case in seed-bearing plants ; but that the fertilizing influence 

 is imparted to the pistil or sporangium itself, when that body is in its 

 most elementary form, long before any spore is produced in its sub- 

 stance, and even when it is itself scarcely to be distinguished from an 

 ordinary cell. Antheridia, as the supposed fertilizing organs are 

 called, are most readily seen among the Fucacece, and will be described 

 under that family. 



Besides the reproduction by means of proper spores,^any Algas 

 have a second mode of continuing the species, and some even a third. 

 Among the simpler kinds, where the whole body consists of a single 

 cell, a fissiparous division, exactly similar to the fissiparous multipli- 

 cation of cells among higher plants, takes place. This cell, as has 

 been already mentioned, divides at maturity into two parts, which, 

 falling asunder, become separate individuals. Similar self-division 



