PLANTS OF THE LOWER GRADE. 61 



multiplication of which the whole fabric was built up. All our or- 

 dinary herbs and trees, however, even while in the seed, have already 

 passed beyond this stage, and consist at this time of a mass of cells, 

 more or less distinctly wrought into the form of a plantlet ; while 

 the germs of plants of a lower grade, at the time of their separation 

 from the parent plant, are each no more than a single cell. Cells of 

 this kind, destined to give rise to new individuals (i. e. for reproduc- 

 tion), are called Spores. The name spore is from a Greek word, 

 meaning the same as seed. 



98. Plants may be distinguished, therefore, into two great Series 

 or Grades, a lower and a higher ; — the lower or simpler grade con- 

 sisting of those plants which directly spring from single cells or 

 spores ; the higher grade, of those which spring from seeds. 



Sect. I. Plants of the Lower Grade; THEnt Develop- 

 ment FROM THE Cell. 



99. This grade includes the simplest and minutest plants, and 

 also many which attain a great size, and exWbit no small complexity 

 of structure, such as Tree Ferns (Fig. 100), for instance. The 

 very lowest kinds not only begin their existence as single cells, but 

 continue so throughout their whole gi'owth. The most simple possi- 

 ble form of vegetation therefore consists of 



100. Plants of a Single Cell. In these minims of the vegetable 

 world, the plant is reduced to its lowest terms : the pla7it and the 

 cell are here identical. The cell constitutes an entire vegetable with- 

 out organs, imbibing its food by endosmosis (40) tlu-ough its walls, 

 assimilating this food in its interior, and converting the organizable 

 products at first into the materials of its own enlargement or growth, 

 and finally into new cells, which constitute its progeny. Thus we 

 have an epitome of all that is essential in vegetation, even on the 

 largest scale ; namely, the imbibition of inorganic materials ; their 

 assimilation; their appHcation to the growth of the individual, or 

 nutrition; and the formation of new individuals, or reproduction. 

 Every stream or pool of water abounds with such plants, often in 

 great variety. Simple as these plants are, they are by no means 

 restricted to one monotonous pattern : perhaps they present as great 

 diversity of form as do the kinds of ordinary vegetation, although 

 from their minuteness they are mostly invisible to the naked eye. 



6 



