Maulu 9, 1883.] 



KNOWLEDGE 



143 



A NATURALIST'S YEAR. 



By Grakt Allen. 

 VIII.— SNOWDROP AND SNOWFLAKE. 



1"^HE little seaward combe where I am wandering tliis 

 morning on a botajiiziug expedition is the only spot 

 in England where the spring snowfluke grows truly wild of 

 its own accord in the open meadows. There are other 

 places, no doubt, where it has spread a little as a straggler 

 from modern borders, or as a survivor from old cottage 

 gardens, and where it lingers on for a few years in a pre- 

 carious fashion ; but, in this sheltered nook of the Dorset 

 downs where I have come to search for it to-day, it has 

 sprung up afresh, season after season, for many years 

 together ; and as it grows in company with several other 

 rare southern species of half-naturalised English flowers, 

 there can be little doubt that, however it originally got here, 

 it finds the climate quite mild enough to suit its tender 

 constitution. It may have escaped from cultivation ages 

 since, perhaps from the grounds of the old monastery in the 

 glen beneath ; or it may have been cut off in this its 

 furthest outlying habitat far earlier stUl, -when the waters 

 of the sea first slowly wore their way through the bed of 

 the English Channel, leaving this little colony isolated all 

 alone from the rest of its kind elsewhere ; but at any 

 rate here it is, and as one more acquisition to the scanty 

 British flora, we may welcome it heartily without inquir- 

 ing too critically into its doubtful antecedents. You will 

 not And it described as British in any of the text-books, 

 however ; for it is not held to have acquired letters of 

 naturalisation as yet ; the only snowflake acknowledged as 

 a true denizen of England by the flora-writers is the 

 summer species, which flowers later in the season, with a 

 cluster of four or live white blossoms at the top of each 

 slender green stem, instead of a single bell only, as in this 

 earlier species. That summer snowflake grows more abun- 

 dantly in many parts of south-eastern England, and so has 

 been fairly adopted into all our handbooks ; but it is not so 

 convenient a flower for comparison with the snowdrop as 

 its spring sister, both because it does not so nearly ap- 

 proach it in character, and because the two do not flower 

 together at the same time. Though the wild spring snow- 

 flake is so rare, it is easy to get at garden specimens, both 

 of it and the snowdrop ; while I know few more instruc- 

 tive lessons in what is called biological specialisation than 

 that which can be gained by comparing together these two 

 closely similar white blossoms. 



Both the snowdrop and the snowflake belong to the 

 family of amaryllids ; that is to say, they are lilies some- 

 what artificially separated from the remainder of the lily 

 group, because their corolla-tube has so grown up around 

 the central portions of the flower as to completely enclose 

 the fruit, thus producing what is called an inferior ovary. 

 If such lilies still possess the normal number of six stamens 

 each, arranged in two whorls of three apiece, they are 

 known as amaryllids; while, if one whorl has been sup- 

 pressed, so that there are only three stamens altogether, 

 they are rather needlessly separated under the name of 

 irises. Now, the spring snowflake may be accepted as a 

 very good typical specimen of the simplest amaryllids. It 

 has three sepals or calyx-pieces, and three petals or corolla- 

 pieces ; only, as in so many other plants of the great lily 

 alliance, these two whorls exactly resemble one another in 

 colour and texture, and cannot be distinguished save by 

 the fact that three of the pieces overlap the other three at 

 the base, thus just suggesting the underlying diffierence 

 between the outer and the inner row. Each such perianth- 

 piece is a dull white in hue, tinged with faint green near 



the tip. The snowflake is a pretty, graceful flower; but it 

 is a decidedly simple and undeveloped type of primitive 

 amaryllid. 



The snowdrop, on the other hand, exhibits the self-same 

 type a good deal more advanced and specialised in the 

 flower, evidently through the agency of higher insect 

 selection. In all other particulars the two plants resemble 

 one another very closely. Both have bulbs containing the 

 store of underground nutriment which enables them to 

 blossom so early in the season ; both have long narrow- 

 leaves, those of the snowdrop umch like the foliage of the 

 crocus, those of tlie snowflake a little more like a small 

 narcissus ; and both have a tall scape, surmounted by a 

 little green sheath or spathe, papery in one part and fleshy 

 in another, enclosing a single drooping flower, and thus 

 testifying very clearly to their common descent at no very 

 remote period from a similar ancestor. But the actsal 

 blossom of the snowdrop shows many marks of higher 

 development which admirably illustrate Mr. Herbert 

 Spencer's law that evolution runs from the homogeneous 

 to the heterogeneous, and from the indefinite to the definite ; 

 or, in simpler words, from the like to the unlike, and from 

 the vaguer to the more distinctly marked. 



First of all, look at the outer perianth pieces. In the 

 snowflake all six are almost exactly alike in shape, size, 

 and colour, being whiteygreen in hue, and pointed in form. 

 But in the snowdrop, the three outer pieces have been 

 dillerentiated (to use Mr. Spencer's word) from the threi' 

 inner ones in all these particulars. They have grown longer, 

 rounder, and more purely and delicately white. All the 

 green tinge that they liad in the snowflake has here dis- 

 appeared, and the sepals of the snowdrop are as pure and 

 spotless in hue as the snow itself from which they take 

 their name. Observe, too, the way in which they bend out 

 and in again, so as to mark themselves off very definitely 

 from the pieces within. And yet note that, without some 

 initial difl'erence of position, this greater final difference of 

 appearance and function could never have been brought 

 about. The snowflake has three outer pieces just dis- 

 tinguishable from its three inner ; and on that prime 

 contrast of position selective action has gradually wrought 

 all the rest. 



Next, look at the three inne. segments in the snowdrop. 

 Here one sees at once that the originally similar and 

 pointed pieces have grown smaller and rounder, and have 

 been notched at the ends instead of being sharpened, 

 so that they now form a ijuite distinct and unlike inner 

 whorl. Once more the indefinite greenness at the end 

 of the petals and sepals in the snowflake has here disap- 

 peared entirely from the sepals, but it has been intcnsilied 

 and rendered far more definite in the petals. On their 

 outer surface, the green pigment assumes a crescent shape, 

 beautifully diversifying the two whorls, and clearly marking 

 for the bees the position of the honey-bearing part of the 

 flower. On the inner surface of the petals, again, the dif- 

 ference is even more marked ; for here we get a series of 

 distinct and parallel little green lines, with white inter- 

 spaces ; and these green lines act as direct honey-guides, 

 leading the bees straight to the nectar gland at the base of 

 the petals. There can be no doubt that the cause operating 

 to produce this change towards greater unlikeness and 

 definiteness of parts is the selective action of insects. They 

 have constantly chosen for unconscious fertilisation in 

 their honey-seeking excursions those flowers in which thoy 

 could most easily discover the whereabouts of the nectar, 

 and have thus produced all those features of the snowdrop 

 in which it differs conspicuously from its snowflake-likc 

 ancestor. 



At the same time, we must not imagine that the existing 



