CHAPTEE XIII. 



Protoplasm and its Properties.^ 



160. The Cell in its Simplest Form. — Sufi&cient has been 

 said in the preceding chapters, and enough tissues have been 

 microscopically studied, to make it pretty clear what vege- 

 ta"ble cells, as they occur in iiowering plants, are like. But 

 in studying the minute anatomy of bark, wood, pith, and 

 other tissues, the attention is often directed to the cell wall, 

 without much regard to the nature of the cell contents. Yet 

 the cell wall is not the cell, any more than the lobster-shell 

 or the crayfish-shell is the lobster or the crayfish. The 

 protoplasm is the cell.^ The cell, reduced to its lowest terms, 

 need not have a cell wall, but may consist simply of a mass 

 of protoplasm, usually containing a portion of denser con- 

 sistency than the main bulk, known as the nucleus. 



Such cells, without a cell wall, are not common in the 

 vegetable world, but are frequently met with among animals. 



161. The Slime-Moulds.^ — The best example, among plants, 

 of masses of naked protoplasm leading an individual exist- 

 ence is found in the slime moulds, which live upon rotten 

 tan bark, decaying wood, and so on. These, like most flower- 

 less plants, spring from minute bodies called spores, Mg. 102, a, 

 which differ from the seeds of flowering plants, not only in 



1 If the teacher prefers to complete the study of the structure and functions of 

 flowering plants before taking up lower forms, he may omit the present and the 

 following chapter until after the flower and the fruit have been studied. It seems 

 better to the author, however, to introduce the morphology and physiology of cells 

 as individuals pretty early, and there are many reasons for taking up these topics 

 immediately after Chapter IV. 



» See Kemer and Oliver's Natwral Bistory of Plants, vol. I, pp. 21-51. 



» Strasburger, Noll, Schenk, and Schlmper, Lehrbuch, pp. 42, 43 and 260-263. 



