Our school greenhouse is filled with life at the moment.  Everything has burst into action growing new shoots and roots.

Although epiphytic orchids live on trees their roots do not penetrate the tree.  They just hold the plant in place and absorb water from rain.

The Aerides odorata cuttings, taken when we cut up our large specimen plant, are growing really well and have started to grow some fantastic new roots .

Pseudolaelia corcodavensis is looking much tidier since the students attached it to a large piece of cork bark. Below is a close up of its new shooting roots.

Orchids are living proof that roots do not always grow down. Grammatophyllum speciosum, the largest orchid in the world has sharp spiky roots that definitely grow up.  They have evolved to catch leaf litter so that the orchid has its own compost. This massive orchid is hungry and each week it is given extra plant food to keep it growing happily.

Here is a close up of those sharp, spiney roots.  More like thorns than roots.

Our large Cymbidium tracyanum also has roots that grew up and they do tend to collect litter from around the greenhouse.

Vanda coerulia, shown below, has roots the width of a pencil.

Epiphytic orchid roots or stele have a protective covering called velamen.  This is a covering of spongy cells that soak up water and send it to the centre of the root, which in turn, transport the water into plant.  Below is a photo of a phalaenopsis orchid root that has been accidentally damaged.  It clearly shows the stele and the velamen.

Healthy roots are firm to the touch.  If an orchid is dehydrated the roots will shrivel and appear silver in colour.  When watered the spongy outer cells will take in the water, expand and turn from silver to green.

Did you know epiphytic orchid roots have another function too like leaves and stems they photosynthesise.