microphotography.
Delafield' s Haematoxylin and Safranin or Bismark Brown
appeared most satisfactory for this purpose.
INTRODUCTION
TILLER PRODUCTION
A grass crop comprises a popula t i on of individual t il le rs , e ach capable of
growth and vege ta t i v e reproducti on and w i th a fini te l i fe . As such i t is sub j ect e d
t o the n ormal dynamics of any popul at i on in which indi v i dual t i l l ers ad j us t t o varyi ng environmental condi t i ons and t o i nter -relat ionships wi t h other t i l l e rs i n
t he s ame hab i t at .
The amount o f growth from a t il l e r and i t s rate o f vege t at i ve reproduct i o n ,
are d e t ermined n o t only by t he avai l ab i l i ty of nutrients , l i ght and moistur e , but als o by compe t i t i on from other t il l ers .
Whe t her the l i fe span o f an indi v i dual t i ller can be measured i n we eks , months , or years , is dependent on the genet ic makeup o f the species concerned and by general environment al condi t i ons , includi ng cr op management .
The ob j ect ive o f this as pect o f the study was to foll ow quant i ta t i ve changes occurring in t i l l e r numbers from sowing unt il the autumn of the s econd year .
LITER ATURE REV I EW
In the Gram i ne ae the se edling eme r ges as a s i ngle shoot wi t h an ext remely
short s t em bear i n g l eaves in oppos i t e ranks . I n the axil o f each l e a f , buds are
produce d . From these , ax i l l ary shoots or t i l lers are forme d . ( Langer 1 963}.
For the produc t i on of i t s firs t t i ller a shoot appears t o require a cer t ain
mi nimum number of leaves . Langer ( 1 96J
)
states that in t imothy about 5 leaves ar� normally v i s i b l e be fore the firs t t i ller appears , but in ry e grass t i l l e r i ngcan occur as s oon as t here are 3-4 expande d leaves on the main s hoot . ( Whyt e e t al
1 959).
I n grass es , the coleopt i le or primary t iller may produce l a teral branches and these in turn other t i l l ers . Under favourable condi t i ons , there fore , s e veral dozen t i l l ers may be formed from a s i ngle s e e d . A s t h e int ernodes are much
shortene d , the branches appe ar t o come out at one point ( R ob b i ns 1 92 4 ) .
T i l l ers grow e i ther upwards within the sheath of the sub t ending l e a f ( i nt ra- vaginal ) as in pra i r i e grass or may bur s t out through the bas e of the l ea f sheath
( extra -vaginal ) as in ry egrass and t i mothy .
Langer ( � 9 6 3 ) s t a t e s t hat , fol l owing i t s appearan c e a t i ller n or mally produces
I
i t s own advent i t i ous root sys t e m , al t h ough i t may remain in vas cular c onne c t i on wi th
the par e n t plan t . The q u es t i on o f whet her t il l e rs func t i on as i ndepe ndent units or whether they are phys i ol og i c ally i n t e r dependent has not been conclus i vely answer e d .
However Barnard ( 1 964 ) has shown that e ve ntually they b e c ome independent , and i n turn supply carbohy drat e s t o t il lers devel oping in the axi ls of their l ower leaves .
However , Barnard does not spec i fy even approximate times following format i on when t i l l e rs may c ont i nue the i r m orphologi cal devel opment as independent uni t s .
Langer ( 1 9 6 3 ) has pres e n t e d a r e vi ew o f fac t ors affe c t ing t i ll e ring i n herbage
gras s e s i ncluding both gen e t i c and environmental e ffec t s .
Mos t studies on t i l l e r i ng in grasses have been made under c ontro l l e d condi t i ons ,
many w orkers havi ng undertaken s tudies wi th s i n gle plants . Few workers have
studi e d t illering in the fi e l d .
Results o n the e ffec t o f cut t i ng and grazi ng o n t illeri ng are s ome t imes
di fficult t o interpr e t , s i n c e a number o f fac t ors may confl ict with o r ass i s t t iller produ c t i on . These include removal o f elongate d s tems ( Langer 1 956 , 1 96 3 ,
� �
de Booys e n � 1 963 ) , t e mpera t ur e ( Mi t che ll 1 953a ) , l i ght intens i ty ( Alberda 1 965 ,
Brougham 1 9 59 ) , grazing s e verity ( Mi t chell & Gl e nday 1 958 , Donal d 1 939 , Lambert 1962 , Langer 1 96 ? ) and mineral supply ( not ably nit r o gen ) ( V os e 1 96 0 , Langer 1 959 b ) . As
Langer ( 1 959b ) sugges ts , inc reas e d t i ller produ c t i on may als o be at t e n de d by a high
death rat e , ind i cating s ev e r e c ompe t i t i on e ffec t s .
Under cont roll e d c on di t i ons s everal workers have shown that unless flowe r i ng st ems are removed , de fol i at i on is unli kely t o i nc rease t illering in s i ngle plan t s ( Mi t chel l 1 953a , M i t chell & Coles 1 955 , and L�nger 1 9 6 J ) .
Perennial herbage gras s es produce many more t illers than are capable o f reaching t h e fl owering s t age . Langer & Ryl e ( 1 959 ) have shown t he abi l i ty o f
t ill ers t o produce ears d e c l i nes t h e later they appe ar , irrespec t i ve o f t h e t i me o f
s owi ng . The pos i t i on o f a t i ller al s o plays a part , t i llers i nsert e d on the mai n
s t e m tending t o have a h i gher chanc e o f flower i n g than ot her t illers on the same