662 PROCUMBENT AND FLOATING STEMS. 



existing stem. At first the new portion of tlie stem is directed upwards, but after 

 a year it lies flat on the ground or is actually 2:)ressed to it. It then sends out 

 lateral branches which repeat the method of growth just described, but it always 

 remains fresh and vigorous, serving for years after it has thrown off its leaves for 

 the conduction of food from the ground and only dies oft' very gradually and 

 slowly from behind. 



In many forms belonging to this first group the older portions of the stem 

 become lignified, and persist for a very long time. They may also increase in thick- 

 ness, exhibiting numerous annual rings, as, for example, the stems of procumbent 

 willows clinging to the rock terraces of the high Alps, as illustrated on p. 524. The 

 elongating stems do not often throw out additional roots, as may easily be shown 

 by raising the stems from their procumbent position. When such stems branch, 

 and the liranches have spread far and wide over the soil, they form an actual 

 carpet, which can be raised from the ground or from the rock terrace as a coherent 

 mass, as, for example, in the red Bearberry {Arctostaphylos Uva ursi) and the 

 white Dryas (Bryas octopetala). Many members of this group possess evergreen 

 foliage, as we see in the Trailing Azalea (Azalea jyrocumbens) and Globularia 

 cordifolia. The Cinquefoils with trailing woody stems (e.g. Potentilla nitida 

 and Clusiana), Sibbaldia (Sibbaldia procumbens) and several valerians (e.g. Vale- 

 riana tripteris and montana), similarly provided, possess, however, no evergreen 

 foliage, and may be distinguished from those named earlier by the fact that the 

 annual increase of their stems is very slight, in consequence of which the older plants 

 have usually a turf-like appearance. Many sjDecies of Thyme (Thymus) are, on 

 the contrary, characterized by the fact that they every year develop fairlj^ long and 

 thin whip-like shoots which weave over the mossy substratum, or, like Dryas, form 

 a carpet on the rocky bed. The stem of the forms hitherto lirought forward is 

 termed " prostrate " (stir2is prostrata), from which is distinguished the " creeping " 

 stem (stirps rej^ens). Even when it has lost its leaves, the creeping stem is not 

 lignified, but develops abundant root-fibres close behind the growing -point, which 

 penetrate into the ground, and often draw the stem down into the soil or mud. 

 The growths of former years do not here persist so long as in plants with woody 

 prostrate stems; they usually die off" after three or four yeai'S, and decay and vanish 

 away altogether. Thus one might almost imagine the stem had been shifted en 

 masse, that it had cremst forward in the direction of the growing tip. Sometimes 

 on the older portions of these stems, the situations where leaves were formerly 

 inserted are mai-ked by transverse scars and bands — reminding one verj- much of 

 creeping worms and caterpillars. The umber stems of the Californian Saxifrac/a 

 peltata which creep over damp rocks by the sides of streams are very striking 

 in this respect. A likeness to worms crawling over the soil is also possessed by 

 the stems of the European and American Asarabacca (Asarum Eitropcsiirii and 

 Canadense), by those of the marsh-inhabiting Buckbean (Menyanthes trifoliata), 

 of the Snake-root (Calla jmlustris), of the purple Marsh Cinquefoil (Comarum 

 palustre), and of several species of clover (e.g. Trifolium repens amd fi^agiferum). 



