ENDOGENS. 285 
Crass IV.—EnpocEns, or Monocory.epons. 
Endogenous or Monocotyledonous plants are herbaceous, very 
rarely woody plants ; Ruscus aculeatus being the only species with 
woody fibres indigenous to this country. Schleiden, 
in describing the peculiarities of Endogens, and 
the manner in which they differ from Exogens, 
says that all plants whose development proceeds 
from the interior to the exterior are either limited 
or unlimited in their growth. Woody fibre gene- 
_ Tally assumes two different physiological phases: . 
1, Of an extremely delicate tissue, capable of 
rapid development, in which new cells are con- 
tinually generated and deposited in two different 
directions, as in Fig. 349; namely, next the cir- 
cumference when the tissue is of a peculiar *} 
lengthened kind, with thick walls and liber; and 
next the centre in the form of annular, spiral, 
teticulate, or porous vessels; 2. Of woody cells, 
Which form wood properly so-called. Up to a 
certain point the development of the vascular 
system is the same, but in Endogens the active 
skin and delicate cellular tissue suddenly change, 
the partitions of the cells become thicker, then the 
Senerating power ceases ; and when fully enveloped 
they assume a peculiar form, cease to convey _ 
any kind of formative sap, and all further de- ky Veda 
velopment of vascular bundles becomes impossible, and there- 
fore the production of woody bundles is limited. In Exogens, 
on the contrary, this tissue retains its vital function during the 
whole life of the plant. 
The general characteristics of Endogens are a fructification 
*Pringing from a stem; wood youngest at the centre ; cotyledous 
‘ingle leaves parallel, veined, permanent ; wood of the stem always 
sed, and indistinct in its fibre. a. 
Endogens consist of 1,420 genera and 13,684 species, whose 
Setmination is endorhizal, whose embryo has but one cotyledon, 
o 
