PhD student Marina Scalon made gas exchange measurements on the leaves of three mistletoe-host species pairs as part of her research. Afterwards, I collected some of the haustoria (the modified roots of the parasite that penetrates the host) and made cross sections from a few.
These are some of the same specimens used to collect the data for the Botanical Vampires prac. Can you identify the parasite (mistletoe) and host in each picture? I’ve labelled some already. Can you see differences between the mistletoe and its host – perhaps in bark or wood properties? Can you identify the haustorium and how the modified root of the parasitic plant has grown into its host? Click on each image to see a larger version.
In the numerical exercise in this prac, Decaisninasignata on Xanthostemonparadoxus was the only species pair in which the transpiration from the mistletoe was significantly higher than the hosts. Look at the cross-sections through the haustoria of the mistletoe pairs and see if you can come up with a hypothesis for why this pair might be different to the other two. How would you design an experiment to test your hypothesis?
Julia Cooke 
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