CHAPTER II. 



THE PLANT-CELL. 



13. — In some cases plant protoplasm lias no definite or 

 constant form. This is its permanent condition in some of 

 the lowest plants — e.g., the M'yxomycetes. In most other 

 lower plants, and in all the higher ones, it has this condition 

 only temporarily, if at all. In the great majority of cases, 

 however, the protoplasm of which a plant is composed has a 

 definite, and, within certain limits, a constant form. It usu- 

 ally appears in more or less rounded or cubical masses of 

 minute size, and which may or may not be surrounded by a 

 cell-wall. In this condition it constitutes the Plant-Cell. 



The undiiferentiated protoplasm of the Myxomycetes reminds us of 

 the lower Monera among animals. In Bathvbius and Protamoeba the 

 naked protoplasm of which they are composed has no constant form. 

 In Protomyxa we have a few simple transformations which are in evei'y 

 respect comparable to those of the Myxomycetes.* In higher animals 

 the protoplasm exists in minute and definitely marked masses, termed 

 cells, or corpuscles, and these have been shown to lie the exact homo- 

 logues of the cells of plants. 



14. — While in young cells provided with a waU the* pro- 

 toplasm fills the whole cavity, as in A, I'ig. 2 (p. 3), in 

 older ones it never does so, and generally these contain only 

 a very small portion of it, as a thin layer covering the inner 

 surface of the cell-wall {B and G, Fig. 2). Close examina- 

 tion shows that this protoplasmic sac consists of (1) a firmer 

 hyaline layer, the ectoplasm, which is in contact with the 



* See further on this subject in paragraph 333, Chapter XI. For a 

 short account of these interestinfr animal forms mentioned above, the 

 student is re''erred to Dr. Packard's "Zoology for Students and Gen- 

 eral Headers," (p. 18 et nen.) in the series of which the present work 

 forms a part, and his " Life-Histories of Animals," where are also given 

 numerous references to fuller accounts. 



