White acetylene

The poet's image is a response to the dazzling effect of the foamy white blossom as it blazes from the bare twigs of the blackthorn round about now, often coinciding with a chilly spell known as the blackthorn winter. That the leaves follow on after the flowers gives the bushes a striking appearance like fresh snow fallen on dark soil.

Blackthorn is a classic of the British countryside and I wasn't surprised to find that the famous Arts&Crafts designer William Morris had created in 1892 a fabric design called Blackthorn, featuring the blossom along with other seasonal flowers - fritillaries, violets, wood anemones etc. (never mind that he or his designer had assigned it 6 instead of the correct 5 petals, maybe we can put that down to artistic licence for the sake of symmetry or something.) 
 Anyway in the hope of getting some more information about the design  I went to the Victoria & Albert Museum website only to find it baldly stated, alongside the image of the wallpaper:
"Portion of 'Blackthorn' wallpaper, a pattern featuring stems of Common Hawthorn, with flowers, and a variety of others flowers with foliage"
Can you believe it? It's called Blackthorn, it IS blackthorn (because you can see the incipient leaves emerging along the bare twigs) but some ignoramus has called it Hawthorn, a  closely-related bush that flowers, as May blossom,  two months hence, with full foliage - as any fule kno. This is  the effing V&A, not some clueless outfit that peddles fake facts! Except that they do.

So, as soon as I have finished my second boiled egg I shall take up my trusty fountain pen, get out my headed note paper and write to The Times... oh, and I could swear I heard a cuckoo yesterday.