662 PROCUMBENT ANO FLOATING STEMS. 



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

 a year it Hes flat on the ground or is actually pressed 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 off 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 liigh 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 bi'anch, 

 and the bi-anches have spread far and wide over the soil, they form an actual 

 carpet, which can be raised from the ground or from the rock ten-ace as a coherent 

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

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

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

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

 and Clusiana), Sibbaldia (Sibbcddia 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 species of Thyme {Thymus) are, on 

 the contrary, characterized by the fact that they every year develop fairly 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 brought forward is 

 termed " prostrate " {stirps prostrata), from which is distinguished the " creeping " 

 stem {stirps repens). 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; thev usually die off after three or four j-ears, and decay and vanish 

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

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

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

 inserted ai-e marked by transverse scars and bands — reminding one very much of 

 creeping worms and caterpillars. The umber stems of the Califoruian Saxifraga 

 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 {Asariun Europceum and 

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

 of the Snake-root {Calla palustris), of the purple Marsh Cinquefoil {Comarum 

 palustre), and of several species of clover {e.g. Trifolium repens &nd fragiferum). 



