## Root length measurements

### Description

Data stem from an experiment assessing the inhibitory effect of secalonic acids on plant growth.

### Usage

data(secalonic)

### Format

A data frame with 7 observations on the following 2 variables:

`dose`

a numeric vector containing dose values (mM)

`rootl`

a numeric vector containing root lengths (cm)

### Details

For each dose the root length is an average three measurements.

### Source

Gong, X. and Zeng, R. and Luo, S. and Yong, C. and Zheng, Q. (2004) Two new
secalonic acids from *Aspergillus Japonicus* and their allelopathic effects on higher plants,
*Proceedings of International Symposium on Allelopathy Research and Application, 27-29 April,
Shanshui, Guangdong, China (Editors: R. Zeng and S. Luo)*, 209–217.

Ritz, C (2009)
Towards a unified approach to dose-response modeling in ecotoxicology
*To appear in Environ Toxicol Chem*.

### Examples

## Fitting a four-parameter log-logistic model
secalonic.m1 <- drm(rootl ~ dose, data = secalonic, fct = LL.4())
summary(secalonic.m1)
## Fitting a three-parameter log-logistic model
## lower limit fixed at 0
secalonic.m2 <- drm(rootl ~ dose, data = secalonic, fct = LL.3())
summary(secalonic.m1)
## Comparing logistic and log-logistic models
## (Figure 1 in Ritz (2009))
secalonic.LL4 <- drm(rootl ~ dose, data = secalonic, fct = LL.4())
secalonic.L4 <- drm(rootl ~ dose, data = secalonic, fct = L.4())
plot(secalonic.LL4, broken=TRUE, ylim=c(0,7), xlab="Dose (mM)", ylab="Root length (cm)",
cex=1.2, cex.axis=1.2, cex.lab=1.2, lwd=2)
plot(secalonic.L4, broken=TRUE, ylim=c(0,7), add=TRUE, type="none", lty=2, lwd=2)
abline(h=coef(secalonic.L4)[3], lty=3, lwd=2)