THE STEM OF VASCULAR PLANTS. 135 



parasites, although it is very difficult, and sometimes 

 impossible, to discover it by a direct examination of their 

 roots. 



Woody Stems are generally devoid of stomata even in 

 their youngest state, and their external cellular tissue is 

 sensibly elongated ; we must, however, except from this 

 rule those which have no leaves, and the green and her- 

 baceous stems of which contain them instead ; such as 

 Ephedra, certain Brooms, Casuarhia, &c. : these branches 

 bear the stomata in the depressed lines, or between the 

 striae. 



Stems, considered as to their general direction, present 

 well marked differences in the various species ; all those 

 which are sufficiently solid have a tendency in general 

 to be erect, and to rise vertically. Diffijrent circumstances 

 in their organization or consistence cause them to vary 

 their positions ; thus, the stem is commonly said to be 

 Prostrate (prostratus ; coachee), when, instead of being 

 elevated, it lies more or less spread upon the ground : this 

 position may occur, either in the principal stems, when 

 they are too weak to support themselves, or in the 

 lower branches, which, in certain plants, diverge at the 

 base horizontally from the stem, so that the principal stem 

 is but little or not developed ; then it appears prostrate, 

 but it is in reality the lower branches which deserve this 

 name. In all these cases, the ends of the stem or 

 branches have a tendency to regain the erect position ; 

 when, in doing this, and in elongating, they remain soft, 

 they fall down again by the base, and continue prostrate ; 

 but it frequently happens that after the first period of its 

 development, a stem so feeble in its infancy as not to 

 be able to support itself, afterwards becomes sufficiently 

 solid to become erect ; it then has the base prostrate, 

 and the summit erect : in this case the name of Ascend- 

 ing (ascend ante, montante) Stem has been given to it. 



