28. In passing from the condition of motion to that of repose, or, in other words, in germi nating, the zoospore is not subject to any sus pension of its vegetative activity. From the moment that it is set free from the parent plant to that at which it begins to develope from itself a new plant similar to the parent, it continues to grow uninterruptedly.
29. Of the aggregate zoospore, the best marked example is that which has been fully described in Vaucheria. In comparing the termination of a fructiferous filament of Vau cheria, with the sporangium of Saprolegnia, we can at once satisfy ourselves that these are corresponding structures ; the distinctive dif ference being, that in the one the whole pro toplasma contained in the termination of the tube is collected together to form a single large zoospore, NI, hile, in the other, it is subdivided so as to form a multitude of small ones. In other words, the single zoospore of Vaucheria takes the place of the collection of zoospores con tained in one sporangium of Saprolegnia. This fact is all that we mean to imply by the use of the term aggregate.
30. Zoosporoid bodies.—Among these we in clude the antherozoids of Cutlerm, of the Fu cacem, of the Floridem, and of the Characew. Of the relations of the first two to the true zo ospore in form and development, we have al ready said enough in the preceding pages. Those of the antherozoid of Chara are not so close; and the structure of the organs in which they are developed, differs so essentially from any structure met with in any other family, that it is inexpedient to found any notions of their nature or formal relations upon such slender analogies as may exist. In the case of the Floridem, the correspondence between the antherozoids and the zoospores of other Algm, is still less trace able ; but the peculiar arrangement of the bodies in question — their being always deve loped in different individuals, though in similar positions as regards the org,ans of vegetation— leads us irresistibly to the conclusion that they have a mutual relation, or are in some degree complementary to each other in function; and as we know the production of germs to be the function of the one, it is reasonable to assign their fecundation to the other.
Germs, whose development is dependent on the combination of two organs the reproductive functions of which are complementary each to each.—Of these it is the leading characteristic that they do not necessarily pass at once, as soon as they are set free frorn the parent, into active development. If the necessary condi tions of temperature and moisture are absent, they are capable of remaining in a state of re pose, without losing their power of germina ting. This state may last for weeks, or even for months. Their second characteristic is connected with the first ; viz. that they are always provided with a distinct investing mem brane, on the strength of which their power of resistance to external agents may in part de pend. This is well seen in the spores of the Desruidem and Zygnemacem.
31. There remain a few examples of germ like bodies of uncertain signification,which are included in neither of the above divisions. Such are the various forms which occur among the Floridex, the stationary spores of Sapro legnia, and others, of which, as they are still imperfectly known, sufficient has been said in the preceding pages.