COLONISATION BY OTHER METHODS. 65 



itself moves from one place to another. The history of 

 a Garlic bulb {Allium ursinuvi) is particularly interesting. 

 The seed begins to develop on the surface of the earth, 

 but as soon as germination begins the growing embryo 

 becomes buried in the soil through a peculiar elonga- 

 tion of the stalk of the cotyledon, which carries plumule 

 and radicle to a depth of 3-4 mm. Its subsequent 

 yearly history is as follows : In April a circle of peculiar 

 fleshy roots is formed ; they grow obliquely downwards, 

 and, when they are firmly fixed by root hairs at their 

 ends, they contract, losing about 30 per cent, of their 

 original length ; in so doing they draw the bulb down- 

 wards into the soil. From May to July the green 

 leaves perform their work, and the flowers and fruit are 

 formed. In September another series of roots grow, 

 not downwards, but outwards ; these are thin, they 

 have no power of contraction, and simply absorb 

 nourishment like those of ordinary plants. From 

 November to April is the winter rest, and in April 

 another circle of stout contracting roots is produced, 

 which again drag the bulb downwards. Eventually it 

 comes to lie at a depth of 10-15 cm. 



Dr. Rimbach has given many other examples of 

 similar tugging roots, e.g. those of the Hyacintb, of 

 the Llartagon Lily, of the Snowflake {Leucoju7n\ of the 

 Strawberry, and of Hieracium Pilosella. The Dandelion 

 always forms its leaves at about the level of the soil, 

 because its thick fleshy root contracts every year just 

 as much as is necessary. The Rat's Tail Plantain {Plan- 

 tago major) has from forty to sixty roots each 30 cm. 

 long and i mm. in diameter ; these contract strongly, 

 so as to pull the stem to about 5 mm. below the 

 surface. As the stem dies off below and grows every 

 season at the apex, it is thus able to hold its ground 

 (Br) E 



