OF THE LOWEE GRADE. 



63 



part of their sustenance, — just as a tufted Moss is nourished in part 

 from the underlying bed of vegetable mould which is formed of the 

 decayed remains of its earlier growth. Other one-celled plants 

 enlarge in one direction more than in any other, so becoming oval 

 or oblong, and making a transition to a somewhat higher grade of 

 vegetation, viz. 



102. Plants of a Single Elongated Cell. Such plants maybe con- 

 ceived to bear the same relation to the foregoing, that ducts (57) 

 and wood-cells (53) do to cells of parenchyma (51). For an ex- 

 ample we may take any species of Oscillaria 



(Fig. 84) ; a form of aquatic vegetation of mi- 

 croscopic minuteness, considered as to the size 

 of the individuals ; but these rapidly multiply 

 in such inconceivable numbers, that, at certain 

 seasons, they sometimes color the surface of 

 whole lakes of a green hue, as suddenly as 

 broad tracts of alpine or arctic snow are red- 

 dened by the Red-Snow Plant. If the trans- 

 verse markings of some Oscillarias answer to 

 internal partitions, then they make a transition 

 between one-celled plants and those formed of 

 a row of cells. — Since cells which form part of 

 the fabric of vegetables are sometimes branched 

 (38), we should naturally expect to find, as the 

 next step in the development, 



103. Plants of an Elongated and Branching Cell. Good ex- 

 amples of the sort are furnished by the species of Vaucheria, which 

 form one kind of the delicate and flossy green threads abounding in 

 fresh waters, and known in some places by the name of Brook-silk. 

 These, under the magnifying-glass, are seen to be single cells, of 

 unbroken calibre, furnished here and there with branches (Fig. 89). 

 The branches are protrusions, or new growing points, which shoot 

 forth by a sort of budding, and have the power of continuous growth 

 from the apex. In Bryopsis (Fig. 91), a beautiful small Sea-weed, 

 the branches are much more numerous and regularly arranged; 

 their cavity is continuous with that of the main stem, if we may 

 so call it : in other words, the whole plant, which is by no means 

 minute, consists of a single, repeatedly many-branched cell. And 

 in Codium, another genus of marine Algae, we have an indefinitely 



riG. 84. Two indiyiduals of Oscillaria spiralis, magnified ; one with an extremity cut off. 



