OF THE LOWER GRADE. 



65 



grows by elongating into a thread, one end of which fixes itself to a 

 stone or some other solid body, while the other grows fii-st into a 

 simjile tube, and then sends off branches like its parent. In this 

 way, a plant composed of a single cell imitates not obscurely the 

 upwai'd and downward growth (the root and the stem) of the more 

 perfect plants, or when cells like these, whether simple or branched, 

 form cross-partitions as they grow, in the manner of the Conferva 

 (Fig. 15) used to illustrate this mode of cell-multiplication, they give 

 rise to 



105. Plants of a Single Row of Cells. Most of the thread-like green 

 Alga3 (Conferveae), which abound in pools and brooks, are of this 

 sort. So are the 

 Moulds or Mildew 

 Fungi, of which 

 three kinds are here 

 represented ; viz. 

 the Bread-Mould 

 ( Fig. 92 ), and 

 the Cheese-Mould 

 (Fig. 93), which 

 live upon dead or- 

 ganic matter; and 

 a species of Botrytis (Fig. 94). The latter, and other JNIoulds of 

 the same or of other kinds, feed upon the juices of living plants, and 

 even animals, where they commit great ravages. The too well- 

 known potato-disease, for example, is probably caused by the attack 

 of a species of Botrytis ; a similar species has long been known as 

 the cause of the muscardine, a fatal malady of silk-woi-ms, and the 

 malady which has for several years destroyed a great part of the 

 grape-crop in Europe is caused by another parasitic plant of the 

 same simple structure. The accompanying figures show only the 

 perfect state of these troublesome little plants, or rather their fructi- 

 fication. Their vegetation consists of long and branching threads 

 • (of which a small portion only is represented at the base), which 

 penetrate and spread widely and rapidly through the vegetable, or 

 other body they live on, and feed upon its juices. At length they 

 break out upon the surface, and produce countless numbers of 



FIG. 92-94. Three kinds of Mould, magnified. 92. Tiie Bread-Mould (Mucor, or Asco- 

 phora). 93. The Cheese-Mould (AspergiUus glaucus). 94. Botrytis Bassiana, the species 

 which attacks silk-worms, &c. 



6* 



