PART II. 

 ANATOMY AND HISTOLOGY. 



20. Introductory. The body of a plant, like that of an 

 animal, consists essentially of living matter termed protoplasm. 

 The body may consist simply of a mass of protoplasm, as the plas- 

 modium of the Myxomycetes ; or it may consist of a mass of proto- 

 plasm invested at the surface by a definite membrane which is not 

 protoplasmic (e.g. Phycomycetous Fungi and Siphonaceous Algse) ; 

 or it may consist of a mass of protoplasm segmented into portions 

 by non-protoplasmic partition-walls. A body of this last type of 

 structure may be conveniently distinguished as septate, from those 

 of the two former types which are unseptate. 



On examining the protoplasm of any plant, it will be found to 

 contain certain well-defined protoplasmic bodies termed nuclei ; it 

 is, in fact, the case that all protoplasm is nucleated. In an un- 

 septate body, such as those mentioned above, the nuclei, which are 

 very numerous, are scattered irregularly throughout the proto- 

 plasm. In the septate body of certain plants (e.g. higher Fungi ; 

 some Algse, such as Cladophora and Hydrodictyon) the septation of 

 the body and the distribution of the nuclei stand in no direct rela- 

 tion to each other, the protoplasm being segmented into portions 

 each of which includes a number of nuclei ; such a plant-body may 

 be designated as incompletely septate. In the rest of the septate 

 plants, the septation of the protoplasm and the distribution of the 

 nuclei stand in a direct relation to each other, such that each of 

 the portions into which the protoplasm is segmented contains but a 

 single nucleus ; a plant-body of this structure may be described as 

 completely septate. 



The portions of protoplasm which are delimitated by the septa in 

 the body of a completely septate plant, are, both morphologically 

 and physiologically, units of protoplasm. They are frequently 

 spoken of as ceZ/s, but it is more accurate to reserve this term to 

 the protoplasmic unit together with the wall (cell-icall) by which 

 it is invested. The structure of the body or any part of it can 



