36 ORGANOGRAPHY. 



walled cells, whose length does not exceed their breadth, or in 

 which the proportion of the two diameters does not vary to any 

 remarkable extent. Parenchyma has been divided in various 

 ways by authors, the divisions being founded upon the forms of 

 the component cells, their modes of cohesion, and other pecu- 

 liarities. It will be sufficient for our purpose to adopt the simple 

 arrangement of Schleiden, which is as follows : — 



\. Jncomipletc Tarenchyma is that in which the component cells 

 I are in contact only at a few points, so that numerous in- 

 terspaces are left between their walls ; of this there are 

 two varieties. 



a. 'Round or elliptical Parenchyma. {Figs. 17 and 66.) — This 

 is formed of rounded or more or less elliptic cells ; it com- 

 monly occurs in succulent plants, and in those parts where 

 the tissues are of a lax nature, as in the pulpy portions of 

 leaves and fruits. The name of merencliyma is frequently 

 applied by authors to this form of parenchyma. It is con- 

 nected by various transitional forms with 



b. Spongiform Parenchyma, which consists of stellate cells 

 {figs. 22 and 67), or of cells with an irregular outline pro- 



Fig. 66. 



Fig. 60. 



Round or elliptical 



parcucbyma. 



Fig. 67. 



Spongiform or stellate 



linreiicliyma, 



composed of stellate cells 



with tliree-coriiered 



intercellular spaces. 



duced by projecting rays, and in contact only by the extremi- 

 ties of such rays, so as to leave large irregular spaces between 

 them {fig. 96, c). This occurs com monly in th e tissue at t he 

 under surface of most leaves," and frequently in t he air- 

 passages orplAHta. " 



2. Complete Parenchyma. — This includes all those forms which 

 are composed of cells in perfect contact on all sides, so 

 that no interspaces are left between them. Of this there 

 are three varieties. 



a. Eegular Parenchyma. — This is formed of dodecahedral or 

 I polyhedral cells, the faces of which are nearly equal {figs. 20 

 / and 21). It commonly occurs in the pith of plants. 

 ' b. Fllongated Parenchyma. — This is composed of cells elon- 

 gated in a longitudinal direction so as to become fusiform, 



