LTXXEAX SOCIETY OF LOXDOX. 79 



a much better chance of holding its own, when sm-rounded bv 

 hixuriaut vegetation, than single individuals would have. Colon- 

 ization aho often affords important service by rendering the 

 pollinizatioii of the ovule more certain than would be the case if 

 the plants were thinly scattered as isolated individuals. In the 

 case of rock-loving plants, the cushion-like colonies, so frequent 

 among our rock flora, retain moisture by collecting debris and 

 dust round the thickly-matted offsets. 



It may be well to recall some familiar examples illustrating the 

 advantages secured by this habit of colonization. 



The common daisy {BeUis perennis) affords us a tj-pical example 

 of a plant w hich would certainly be smothered if it grew in a con- 

 dition oi: isolation. Those who have watched this little plant 

 gradually taking possession of their lawn, must have noticed the 

 first unfolding of its rosette of stifl' leaves, either in some thin 

 place upon the lawn, or at an earlier period of the season, before 

 the surrounding herbage has commenced to grow. Having secured 

 its foothold, it quickly sends up offsets which soon clear a com- 

 paratively large space, thus securing an abundance of light and air. 

 The colony rapidly spreads, neighbouring colonies join their forces, 

 until a large portion of the lawn is occupied by our humble friend. 



The short, thick rhizome of the iris {Iris Pseudncorus) co-oper- 

 ates with the rigid sword-shaped leaves to secure light and air for 

 a plant growing under very different circum>tances. Even the 

 rank riverside vegetation is quite unable to resist the force of the 

 growth of these thick rhizomes crowned by rigid leaves. IVor 

 must we overlook the important service rendered by colonies of 

 grasses and sedges on our sand-dunes, in holding the sand together 

 by their matted roots ; but for these matted offshoots no plant 

 could live upon these sands. 



Amongst the wind-fertilized plants, the perennial mercury 

 {MercariaUs jyerennis) illustrates the service rendered by colonies. 

 The seedling plant quickly forms comparatively thick colonies by 

 means of underground stems, and the inflorescence is developed 

 in the early spring before the woodland vegetation has appeared ; 

 orherwise the wind-blovATi pollen of this plant would be obstructed 

 in its passage from colony to colony. One colony produces stami- 

 nate flowers exclusively, another colony produces pistillate flowers 

 only. The colony of staminate flowers sends out clouds of pollen, 

 whilst the pistillate flowers unfold their stigmas gradually, and are 

 thus for a long period ready to catch the pollen as the clouds pass 

 in their direction. It is clear that pollination would be more pi-e- 

 carious if the pollen was produced in small quantities by isolated 

 plants. 



The common stinging-nettle ( Urtica dioica) also forms colonies 

 hi/ mca7is of underground stems, and these likewise send out clouds 

 of pollen which fertilize flowers of neighbouring colonies. 



The wild thyme (Thymus Serpyllum) may be cited as an example 

 of a plant which secures the fertilization of its ovules by the 

 formation of dense colonies. Its flowers would have small chance 



