Growth is dependent on three factors - initial size $\left(W_0\right)$, rate of growth $(r)$ and time interval (+) for which the rate of growth is retained.
Where,
$$ \begin{aligned} W_1 & =W_0 e^{r t} \\ W_1 & =\text { final size }, \\ W_0 & =\text { Initial size }, \\ r & =\text { growth rate, } \\ t & =\text { time, } \\ e & =\text { base of natural logarithim. } \\ 19 & =5 \times(2.7)^{r \times 7} \\ \frac{19}{5} & =(2.7)^{r \times 7} \\ 3.8 & =(2.7)^{r \times 7} \end{aligned}$$
$$ \begin{aligned} &\begin{aligned} \log 3.8 & =r \times 7 \times \log (2.7) \\ 0.5798 & =r \times 7 \times 0.4314 \\ \frac{0.5798}{7 \times 0.4314} & =r=0.1907 \\ \text { Relative growth rate } & =\frac{\text { Growth in given time period }}{\text { Measurement at start of time period }} \\ & =\frac{19}{5}=3.8 \mathrm{~cm} \end{aligned}\\ &\text { Thus absotule growth rate is } 0.1907 \text { while relative growth rate is } 3.8 \mathrm{~cm} \end{aligned}$$
Gibberellins were first discovered in Japan when rice plants were suffering from bakane (the foolish seedling disease) caused by a fungus Gibberella fujikuroi.
(a) Give two functions of this phytohormone.
(b) Which property of gibberellin caused foolish seedling disease in rice?
(a) The hormone, gibberellin
(i) Produce the phenomenon of bolting, i.e., the growth of the internodal region of stem in rosette plants.
(ii) Induces seed germination and break bud and seed dormancy.
(b) The rice seedling/plant show excessive growth in their internodal region when get infected with fungus Gibberella fujikuroi. This fungus produces excessive amount of plant hormone GA which makes plants taller than the normal plant foolishly and many result into death of the plant.
Besides some primary function, both gibberellins and ethylene have some special effect on some specific plants as Gibberellin promotes the formation of male flower an genetically female plants while ethylene promotes formation as Female flowers an genetically, male plants.
Long Day Plant (LDP) Some plants require the exposure light for a longer period exceeding a well defined critical duration of light. Among the above given plant LDP are for flowering henbane, Bryophyllum and spinach.
Short Day Plants (SDP) Some plants flower when and these can blossom throughout the year. expos to light for a period less than well defined critical duration of light. e.g., of SDP are. e.g., Xanthium, rice, strawberry.
Day Neutral Plants (DNP) The exposure to light does not affect the flowering in certain plants, e.g., DNP, are sunflower, tomato, maize.