Whats up with this little guy?

[klip247]

I put this guy in my cupboard after cutting him off the main plant, about 2 weeks later I pulled him out to re-plant and was surprised to see the tip has turned yellow and also has bent the tip in search for light! Anyone know whats going on here with this little fellow?

And here is the "Mother Plant" for reference (I cut it off the main section which is visible behind the pup):

Edited April 17, 2010 by klip247

[PhoenixSon]

he just wants the sun

[Yawning Man]

Careful klip, dont put him in direct sunlight or he'll get burnt. Leave him in the shade and expose him to the sun a little bit at a time.

cheers

[klip247]

Cheers, ive just moved him over into the shade.. wouldnt want him to risk getting burnt.

Edited April 19, 2010 by klip247

[WoodDragon]

Like the others said, it's looking for light.

The yellow tissue is new growth that occurred after the plant was put into darkness. When there is no light on a plant, new chlorophyll tends not to be synthesised: to do so is an energetically expensive drain on the stored reserves of a plant, at a time when it is unable to harvest any new energy from light.

To put so much growth out after being cut the plant must have had a significant growth 'signal' just prior - a whack of warmth, water, nutrients, or a combination of these - that overcame the (extremely!) reduced amount of light.

The bending though is more likely to have resulted from the cactus being placed on its side, rather than from any attempt to "grow to the light". Most arid-zone cacti seem to be more geotropic (roots grow 'down', tips grow 'up') than phototropic (growing toward light), probably because they grow in open desert regions rather than in forested ones, and growing up basically means the same thing as growing toward light. When one mechanism will do, geotropism seems to be a better energetic approach, apparently. Zygos, epis, rhipsalis, lepis and such are somewhat phototropic, and this reflects the fact they are forest dwellers, so both tropisms are useful.

As YM said, a slow progression to light is best. Once the light-deprived tissue is exposed to light, the chlorophyll synthesis will restart, as will the carotenoid and xantho- syntheses, and after a few weeks/months the new growth will be able to handle full light without being burned. I used to put cuttings in the dark myself, but after a bit of thought I decided that good shade is all that is needed whilst the callus forms, and I give them about a week to do that. After a week, I plant them in very dry substrate, give them a few more weeks, and them give just a little bit of water to moisten the soil for a maybe half a day. This seems to encourage roots to come a-lookin', without risking rot. Over the span of a few weeks I gradually add a bit more water, and soon enough the cutting is powering along.

Using this approach, I get lots of roots in just a few weeks after cutting, as long as it's not deep winter - which can be quite 'deep' in my corner of the world!

Of course, if you want to keep the cutting in statis for a few months, just don't plant it. Give it a very indirect amount of light though, and you'll avoid the yellowing that the cutting above demonstrates.

As an aside, one might wonder how a plant actually 'grows' without roots or light. What is happening is that the plant is manufacturing new cells, at the expense of the biomass of the original old cells. There is little overall change in biomass, except what is lost in transpiration and expiration from metabolism.

This way, when more light appears and when more roots form, the plant will be able to 'fill' more cells with juicey goodness, and thus be able to eventually allocate more biomass to fruiting when that time occurs.

Ain't nature wonderful?

Edited April 17, 2010 by WoodDragon

[klip247]

Thanks for the clarification WoodDragon, its great to hear these detailed explanations.. nature sure is wonderful.