INTRODUCTION. 15 



ters. There are three principal modes. In the first, the 

 spore is simply quartered by two transverse lines, cross- 

 ing at right angles at its centre, and is said to be cru- 

 ciate. In the second, it is divided into four unequal 

 parts, three of which only are visible at once, by lines 

 which radiate from the centre, and is called tripartite. 

 The third and last kind is called zonate, and is trans- 

 versely divided. 



The annexed woodcuts of the appearance of the dif- 

 ferent kinds, when highly magnified, will be more easily 

 understood than my imperfect description. 



Kg. I. Cruciate. Fig. 2. Tripaitite. Fig. 3. Zonate. 



The fructification of the Green series is wrapt in 

 greater mystery than even that of the Reds. It con- 

 sists chiefly of zoospores, which have been already de- 

 scribed; but ordinary spores and aniheridia are also 

 developed in certain genera. The existing knowledge 

 of the subject is too imperfect to afibrd the data for 

 a popular detailed description; and, further, it is al- 

 most impossible to separate that part which relates to 

 the marine species from that belonging only to the 

 fresh-water. 



I trust that I have traced a sufficiently clear outline 

 of the mode oi fructification to serve the purpose of the 

 majority of my readers. Those who desire to extend 

 their researches I must refer to the works of Agardh, 

 Harvey, and other writers. 



