THE STEM OR SHOOT. 



81 



Fasciation.* 



1. Ordinary Fasciation. — This is one of the most 

 widely-spread phenomena in the vegetable kingdom, 

 occurring most commonly amongst cultivated plants, 

 but also from time to time in Nature. 



A " fasciated " shoot, whether it be the main stem 

 of the plant or an individual branch thereof, may be 

 described as follows. The shoot affected is, in the 

 majority of cases, if not in all, more vigorous and 

 stouter than the normal ones amongst which it may 

 be growing. At the base, and for a varying distance 

 upwards, it has the usual cylindric contour; sooner or 

 later, however, this becomes more and more flattened, 

 until, in the upper part of the axis, a band-shaped 

 structure is assumed which is due to the great increase 

 in diameter of the stem in one plane only, all the 

 tissues being concerned in this formation, so that in 

 transverse section of the stem the central vascular 

 cylinder would present the appearance, according to 

 the degree of fasciation, of a drawn-out oval instead 

 of the circle which it normally assumes. 



Fasciation may affect the main stem only, all the 

 lateral branches being normal ; or some of the lateral 

 branches, viz., those situated in the plane of the 

 fasciation may be affected like the parent stem, while 

 others, emerging from the latter at right angles to 

 the fasciation, are quite normal. Often individual 

 branches or portions of such are fasciated, while the 

 main stem is perfectly normal, as in the case of many 

 trees, e. g. the ash and sycamore. 



In nearly all cases the fasciated shoot branches 

 above, giving rise to a complex system of secondary 

 fasciated axes, which in their turn may again branch, 

 and so on, sometimes ad infinitum. This branching of 

 the fasciated stem at the apex is of the primitive type 

 known as dichotomy or bifurcation (forking), such as 

 characterizes many Vascular Cryptogams, e. g. the 



* Latin fascia, a banding. 

 VOL. I. 6 



