COLONISATION BY OTHER METHODS. 63 



other hand, the stem of the Bracken is almost perfectly 

 horizontal, and is buried below the ground at a con- 

 siderable depth. Every year it grows forward a 

 few inches and both leaves and roots appear in a 

 new position. 



The diagram here given illustrates some of the 

 different methods of colonising by branches or stems. 



In the Strawberry and Silver-weed {Potentilla Ansei'ina), 

 the branches given off from the main stem are prostrate, 

 or flat on the ground. They root themselves at the 

 tip, forming a new plant. Thus a new base is occupied, 

 and another branch or runner is pushed forward, often 

 in the same line, to occupy a position still further off. 

 Again, underground, such plants as the Iris or 

 Solomon's Seal act very much after the same fashion. 

 A branch grows horizontally underground for a short 

 distance, and then turns up into the air to produce its 

 leaves and flowering stalks ; another branch, starting 

 from the buried part of the first, grows still farther 

 forward, and also sends up leaves, etc. This " sjnn- 

 podial rhizome " method is very common. It will 

 be seen that the principle is the same in the cases 

 of the Male Fern, Sugar Cane and Eose Suckers, but 

 in these the successive branches are formed at 

 greater intervals, so that they do not form the dis- 

 tinct chain of branches, which is easily seen in 

 Solomon's Seal and Iris. This underground colonisation 

 is especially common in weeds. 



The Canadian Thistle of American agriculturists, or 

 " cursed thistle," has an extensive underground system 

 of 7'hizoines and roots, which can produce buds at any 

 point. Pieces of these underground stems only a 

 quarter of an inch in length can reproduce the parent 

 plant. As it is buried at a depth of 6 to 30 inches 



