341 



The CEEEPING ROOTSTOCK of AGROPYRUM REPENS. 



By Margery Knight, M.Sc. 

 Assistant Lecturer in Botany, University of Liverpool. 



(Plate 528 a.) 



Agropyrum (Triticum) repens L., commonly known as couch 

 or scutch grass, has been described as the worst weed of cul- 

 tivation. This undesirable title has been given to the plant on 

 account of the difficulty of extirpating it when once it has taken 

 possession of the soil. The plant is a perennial, and its branch- 

 ing rootstock forms a dense underground tangle or mat, giving 

 off roots below and aerial shoots above. 



The branches of the rootstock end in sharpened apices, which 

 are perfectly rigid, and being pressed forward by intercalary 

 growth of the internodes behind make an excellent boring 

 apparatus. It is quite common to find potatoes transfixed by 

 the rhizome. The forward movement of the sclerotic apices 

 raises the question of the distribution of meristem and its trans- 

 formation into permanent tissue, and Professor Harvey-Gibson 

 suggested to me that it might be worth while to determine 

 precisely the distribution of growth in the shoot apex and the 

 exact nature of the boring apparatus. 



Careful dissection shows that the apex consists of a bud, the 

 leaves of which are inrolled to form a tube ; the tip of the outer- 

 most leaf forms the hard point, and within it follows a series of 

 successively smaller leaves until the actual merismatic stem apex 

 is reached within the youngest leaf (fig. 2). Growth of the 

 second oldest leaf and elongation of the internode below it force 

 the apex through the sclerotic tip of the outer covering leaf 

 (fig. 2). This takes place successively with the progressive 

 development of the shoot ; the older leaves becoming more and 

 more ragged and torn, until, finally, they may be represented on 

 an old stem by jagged ridges only. No sclerenchyma is developed 

 in the leaf until it has almost reached full size and is ready to 

 break through the older covering leaf. The bands of sclerenchyma 

 run longitudinally, and are laid down over and alternately with 

 the vascular bundles. These ribs converge to the tip of the leaf, 

 where they form the sclerotic boring point. While this develop- 

 ment of sclerenchyma is taking place, sharp, backwardly-directed 

 hairs grow out from special epidermal cells ; these are perfectly 

 rigid and, acting like barbs on a fish hook, resist any attempt to 

 tear the plant out of the ground (fig. 9). 



Structure of stem. — In transverse sections the stem shows a 

 central pith, which is more or less destroyed in the internodal 

 regions, surrounded by a double ring of bundles of which the 

 smaller are externally placed. A fairly thick cortex surrounds 

 the vascular tissue ; possibly the aggregation of the sclerotic cells 

 into a ring as near the centre as possible is an adaptation to the 

 kind of strain which an underground stem would have to with- 

 Journal of Botany. — Vol. 51. [Dec. 1913.] 2 d 



