[R-sig-eco] Problem with result PCA

[momadou sow]

Hi, 
I created a PCA (see attached file). I use this code: 
>library(FactoMineR)
>res.pca<-PCA(acp)
 I use satellite indexes and two indexes of vegetation water content (FMC and EWT) measured in field. For the satellite indexes some values are negative while all the values for FMC and EWT are positive. 
Now when I run my code, I see FMC and EWT are in the negative part in the PCA between [0,-1] (please see attached file).
Is it normal to have variables with positive values in the negative part of PCA while the variables with negative values are in the positive part?
Thank you in advance. 
 
Momadou