Re: is there a scientific explanation for the fast growth of radish

Why yes there is a scientific explanation for the fast growth of smaller 
seeded plants like radish.  And you probably want to know what this answer 
is.

Plants like other organisms have many different life strategies.  This 
doesn't mean they consciously decide to do one thing versus another like 
in a football match, but it does mean that natural selection has produced 
different ways to be successful.  

Very generally there are two broad strategies that correlate with seed 
size.  First you must understand that seeds contain plant embryos and 
represent a significant investment by the parental plant.  Since the 
energy available for producing offspring is limited there are two basic 
strategies.  Either make lots of little seeds investing very little in 
each one.  Although their chances of success (surviving until they can 
produce offspring) are low, with so many potential offspring some will be 
successful.  The alternate strategy is to invest more energy in fewer 
offspring via bigger seeds.  This enhances each embryo's chance of 
success, but there are fewer of them.  This type of tradeoff is the result 
of having limited resources.

Weeds are a good example of plants adapted to the small seed, many 
offspring strategy.  Weeds are not good competitors in natural 
environments, they rely on finding disturbed areas where they can invade, 
grow, and reproduce quickly before more competitive, but slower growing 
plants can get established.  Oh, but you know weeds compete with crop 
plants so well that too many weeds can destroy the crop.  This is because 
an agricultural field is a disturbed environment, and in this case, the 
disturbance is caused by human activities and our needs for the crops.

So radishes are a weedier species than beans.  Many mustards, which 
includes radishes, are weedy, adapted for fast growth in disturbed 
environments and production of many small seeds.  The beans are adapted to 
slower growth and production of larger, fewer seeds.

This demonstrates why we must understand ecology and evolution.  Weeds and 
the fast growth of small seeds only makes sense in this context.  So your 
experiment demonstrated a basic biological principle.

But why did you do the experiment in the first place?  Probably you had no 
idea, but your instructor wanted you to observe something unexpected and 
then try to find an explanation.  I would have asked you to generate your 
own hypothesis and then find a means of testing it to discover if you were 
correct or not.  This is how science is done, and this is how science 
should be taught.  When a scientist conducts an experiment we have an 
expected outcome, a prediction, based upon some explanation, an 
hypothesis.  If the experimental results are not as we predicted, then our 
hypothesis must be rejected or revised.  And then we test the new 
hypothesis.  If the results agree with our hypothesis, we gain confidence 
in its truth via confirmation, and so our knowledge grows.  This is why 
evolution is a powerful hypothesis, it accurately predicts so many 
biological phenomena.