Most flowers neatly severed just below the petal’s base

The Crocus chomper next to some Scilla tubergeniana

As we pass St.David’s day with only a few Narcissus ‘Tête-à-tête’ in bloom, we have at least the Crocus to lift the spirits as the temperatures drop, the wind blows from the East, and at last today, dawn till dusk sunshine. But this year, our wonderful display from our favourite Crocus tomassinianus, has literally been cut short. For once I’ve managed to capture the culprit on film, though not actually in the act. What I think is a bank vole has moved through hundreds of blooms, carefully nipping them off just below the globe of the flower.

I’ve become used to Crocus damage in the garden at 2 times of the year, firstly when the flowers emerge, and secondly when the seed capsules push through the ground in late June. Usually prompt dusting with cayenne pepper around the area seems to sort the problem, but this year, because of constant rain I delayed, and have lost most of the first batch of flowers. We’ve been lucky to so far avoid actual corm damage, but it did start me thinking and researching what the vole was actually after, since the corms were left untouched. This led to a fascinating exploration which has raised more questions than answers – perhaps folks can fill me in on my knowledge gaps or correct any botanical howlers. The first thing I established was that in crocus species the ovary, and hence potential seeds, are located below ground level. This led to the discovery that the pollen grains, once transferred to the frilly style, have to grow a pollen tube right the way down to the base of the often 3 inch long flower stalk.

How long for a pollen tube to grow down this to the ovary?

How long does this process take? This is of interest, since this year with very cold weather, and no bumblebees and few flies about, I had hand pollinated the crocus flowers with a small paint brush. If the pollen tubes had grown down to the ovary by the time the vole struck, will viable seed still be produced? The long pollen tube acts as a conduit for the male gametophyte cells to pass down to fertilise the ovules. But I found a reference to the saffron crocus which implied that the only source of nectar was tissues around the ovary, which as we have seen is below ground and hence out of reach of all bees’ proboscis. Apparently nectar can also be produced from glands at the base of the flower petals, but look at the photo of the near vertical honey bee and you can see that its proboscis is probing down beyond the base of the flower…

Vertically aligned proboscis

 The video clip this image was taken from, shows it was desperate to get beyond the point it seemed to be able to reach, before it gave up its efforts. This picture was taken last year in early March, when a number of bees had begun to be active. You can also see from the creamy flowers of ‘Cream Beauty’, that many Crocus varieties are of low fertility and set seed minimal seed – in this case the anthers don’t produce pollen. Still I have to guess that the very particular careful chewing of the vole, which left piles of wilting purple petals amongst leaves on the ground was perhaps after some sweet nectar. Or whether even the nectar had been fermented by a natural yeast to alcohol, and thus a boozy drink (a strategy used by Malaysian palms to attract the only pollinator of its flowers, a tree climbing shrew). Or maybe just the ample pollen grains which C. tomassinianus flowers contain, and which are nutrient rich. (Interestingly, so far the ‘Cream Beauty’ flowers have been left unscathed).

Another point I’ve pondered is the raised temperature inside the crocus flower. Using my little laser digital thermometer today, I could detect temperature rises of about 5 degree C inside the flower, although less in the small yellow crocus. This is widely thought to be of benefit in attracting pollinating insects at this time of the year, when ambient temperature may only be a few degrees C above freezing. The commonly held view is that insects will actively select warmer flowers, since they then waste less energy on keeping their body temperature maintained (bumblebees have a body temperature of about 40 degree C).

All those mites look really itchy

There is an excellent article on this subject which can be found by googling ‘Warm Flowers, Happy Pollinators’, by Whitney and Chittak.

However I wonder whether in addition, this raised temperature aids the growth of the pollen tube over the long distance it has to travel, by providing higher temperatures for enzymic activity. Also it seems that the wineglass shaped flower may well be the perfect way of concentrating any attractive nectar scent – think of balloon glasses for wine or brandy – wherever it is produced from, and thus attracting insects into the flower globe even if they can’t reach the source of the scent.

Wineglass shaped flowers of species Crocus sieberii

Many enzymes (living organism’s critical catalysts) are highly temperature specific and I remember from my homebrewing days how the relative activities of the enzymes maltase and amylase in the barley, the balance of which influences the alcohol content and flavour of a beer, were affected by very slight temperature differences in the range of 62 to 70 degrees C when the malted barley is mashed. (And what are these enzymes doing there, sitting in the malted grains, just waiting to be activated at temperatures which would never normally be achieved without the brewer’s best efforts to heat the soaked barley to these levels?)

Furthermore, following my veterinary nose, the temperature difference of most mammalian testes which results from them being held outside the body in the scrotum, is a mere 2 degree C below normal body temperature. This slight temperature differential in other mammals like elephants, which retain their testicles inside the abdominal cavity, is even achieved by the female elephant’s body temperature rising by the same 2 degree C when she is on heat and receptive to the male. There is even recent speculation that this slight temperature difference between male and female genital tracts is vital to complete the maturation process of the sperm. So very subtle temperature changes clearly have great biological advantages, even though we would be unlikely to be able to detect or register them. (Or would we?)

Crocus ‘Snow Bunting’ in our mossy copse

This same 2 degree C temperature rise is what got me to set up a blog, having been fascinated by Carolyn’s Shade Garden blogpost about possible thermogenesis in snowdrop flowers, and my own trials where I was able to consistently record a 2 degree C temperature change between the inner white petals and the dark green ovary, when one might have expected the darker surface to register the higher temperature.