IV. 
INTRODUCTION. 
13 
artificial green may be imparted to the specimens ; but such a mode of preparation 
of specimens ought never to be practised by botanical collectors, though it may 
sometimes serve the purpose of makers of seaweed pictures. 
THE FRUCTIFICATION 
of the Algae may be more conveniently described in the systematic portion of this 
work, when speaking of the various forms it assumes in the different families. I 
shall at present, therefore, limit myself to a very few general observations. The 
spore or reproductive gemmule of the Algae is in all cases a simple cell, filled with 
denser and darker coloured endochrome (or colouring matter) than that found in 
other cells of the frond. In the simplest Algae, where the whole body consists of a 
single cell, some gradually change and are converted into spores, without any 
obvious contact with others : but far more frequently, as in the Desmidiacece and 
Diatomacece, a spore is formed only by the conjugation of two cells or individual plants. 
When these simple vegetable atoms are mature, and about to form their fructification, 
two individuals are observed to approach ; a portion of the cell- wall of each is then 
extended into a tubercle at opposite points ; these tubercles come into contact 
and at length become confluent ; 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 old cells is transmitted and becomes mixed ; changes 
take place in its organization, and at length a sporangium 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 sporan- 
gium, which may remain dormant, retaining vitality for a considerable time, 
as from one year to another, or probably for several years. These sporan- 
gia, 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 Algse form fruit in this manner, to which the name con- 
jugation is technically given. The thread-like Silk-weeds of ponds and ditches 
{Zygnemata and Mougeotioe , &c.) are good examples of such a mode of fruiting. In 
these almost every cell is fertile, and when two 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, seemingly, no differ- 
ence 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 Algae appears to be very similar : 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 neighbourhood of the fruit cells ; but with the complication of the 
parts of the frond, the exact mode in which spores are formed becomes more difli- 
