THE CELL. 41 



forms in this section. By way of completion we will add some 

 general remarks on cell-forms and their names, since the expressions 

 and terms concerned pertain to the most valuable language-treasure 

 of scientific botany. 



The terms imrencUyma and lyrosenchyma have long been es- 

 tablished. They do not refer to the mode of growth, but simply 

 to the form of the cells. The term iKvmnchyraa is used to 

 designate: 1, all isodiametric and tabular cells (hence all spherical, 

 cubical, parallelepi pedal, and polygonal cells) ; ii, all elongated 

 cells having blunt ends (hence all elongated cells with exactly or 

 -approximately rectangular ends). All elongated cells loith jyointed 

 or sharj) endings (hence conical, one or both ends blade-like) 

 are prosenchymatous. The most important representatives of 

 2)rosenchyma are the mechanical cells (skeleton-cells) which were 

 named " sterome-cells " or "stereids" by Schwendenee. 



With Habeelandt we use the term sclerenchyma ' to designate 

 /considerably thickened non-jprosenckymatoiLS elements which occur 

 isolated or in groups in various tissues exclusive of vascular bundles ; 

 therefore in the outer cortex, pith (medulla), etc. Two sclerenchyma- 

 ■cells in cross-section are shown in Fig. 22. 



A fitting introduction to a brief consideration of the origin of 

 new cells is the statement of a fact which sometimes causes difficul- 

 ties to the beginner in phytotomy; it is that every 

 <^ell has a membrane. This statement holds good 

 for every tissue-structure. On maceration (care- 

 fully boiling, for example, a particle of wood in 

 sulphuric acid and calcium chloride) the tissue 

 separates into its individual elements. Even an 

 immeasurably thin wall between two cells of a ■^^^* ^^• 

 mature tissue is thereby split and shown to be double. The macer- 

 ating liquid has dissolved the cementing material. This leads 

 us to the so-called " primary membrane" or " middle lamella," which 

 is, however, not wholly identical with the intercellular cement. 

 The prominent, not immeasurably thin, middle lamella of woody 

 cells differs from the remaining membrane in having a different 

 refractive index. Solubility in the macerating mixture is therefore 



' De Bary (Comp. Anatomy) designates typical mechanical cells as " scleren- 

 chyma fibres"; hence the terminology here introduced differs markedly from 

 that of de Bary. 



