200 



KNOWLEDGE 



[September 2, 1895. 



belonging to the other sub-classea ; it occurs, however, in 

 the ash, plantain, wormwood, mare's-tail and meadow-rue. 

 The number of wind-fertilized monocotyledons far exceeds 

 those adapted to insects, both as regards individuals and 

 species. The extensive order of grasses, the sedges, carices 

 and rushes, together with the arrowhead, arrowgrass, 

 bur-reed and bulrush, are all without exception auemo- 

 philous. It thus appears that wind-fertilization occurs iu 

 many different and widely separated families. Certain 

 negative characters are common to all the wind-fertilized 

 class ; no honey is secreted, no perfume emitted, and con- 

 spicuous colours are wanting. On flowers of this descrip- 

 tion it is difficult for a large insect like a bee to obtain a 

 footing ; there is no corolla that can serve as a landing- 

 stage for insects to alight. For these reasons anemophilous 

 blossoms are almost entirely neglected by bees and other 

 flower-haunting insects ; only in exceptional instances do 

 visitors have recourse to them in search of pollen, but this 

 is so dry and has so little cohesion that it must be difficult 

 indeed for a bee to collect an appreciable quantity of 

 anemophilous pollen. Wind-fertilized flowers thus offer 

 little or no attraction to insects, and are in no way adapted 

 to derive benefit from their visits. On the other hand, 

 there exist in them a number of provisions which 

 admirably adapt them for cross-fertilization through 

 atmospheric agency. The most important of these is 

 abundant pollen ; always more than in insect-fertilized 

 blossoms, the quantity produced by some plants of the 

 wind-fertilized class is enormous. The so-called showers 



of sulphur, occasionally 

 reported in the news- 

 papers, are really great 

 deposits of pollen blown 

 from the male cones of 

 the Scotch fir. It has 

 been known to fall ou 

 ships at sea, and has 

 been swept up in bucket- 

 fuls from their decks. 

 The common ash dis- 

 charges an immense 

 quantity from its in- 

 numerable flowers, so much so that a person shaking a 

 branch when the tree is in bloom is dusted from head to 

 foot with the dry powdery pollen. That of the elm is also 

 very abundant, and this is more or less characteristic of 

 all plants which depend for cross-fertilization on the wind. 

 At certain seasons the air may be said to be literally 

 charged with the pollen of anemophilous plants. In the 



Fig. 2. — Pollen Grainsof luseet- and 

 Wind-fertilized Floweiv. 1, Coltsfoot ; 

 2, Abutilon ; 3, Wulf's-bane. (Insect- 

 fei'tilized.) 4, Hazel ; 5, Ash ; (i, 

 Planfago ; 7, Grass ; 8, Pine. (Wind- 

 fertilized.) 



FlC. 3. — i.'ule and Female Plants. Dog's-JIerenrv. 



beginning of May I exposed on the window-sill for forty- 

 eight hours a microscopic slide smeared with syrup, and on 



be found 

 number , 



examining it afterwards detected upwards of fifty pollen- 

 grains belonging to various trees, some of which are not to 

 be found within a radius of two miles. The efficiency of 

 the wind as a fertilizing agent is, therefore, much greater 

 than one might suppose. 



The pollen grains of insect-fertilized flowers are fre- 

 quently, as in the harebell, coltsfoot and mallow, studded 

 over with little projecting points ; these cause them to 

 adhere readily to each other or to the hairs of an insect. 

 In other cases the pollen is viscid, and the granules are 

 diflicult to separate. This cohesive character obviously 

 renders them ill adapted for transference by means of the 

 wind ; accordingly the pollen of wind-fertilized plants is 

 excessively light and drj', the granules are smooth, they 

 do not stick together, and this incoherence facilitates their 

 wide dispersion. A special provision exists in the pine, 

 whereby its pollen is rendered lighter and more easily 

 wafted by the wind ; the extine or outer membrane of 

 each granule is inflated into two globular air- sacs, which 

 reduce its specific gravity so that it can keep longer afloat 

 in the air. 



Although there are wind-fertilized species to 

 in bloom almost all the year round, a large 

 especially of trees, blossom early 

 in the season ; the hazel comes into 

 bloom in February, the elm, pop- 

 lar and willow following in March 

 or April. The little flowers of the 

 willow are already developed within 

 the bud at the beginning of winter ; 

 in spring they merely expand. It 

 is, therefore, probable that trees 

 of this class originally flowered 

 towards the end of the year, but 

 ultimately became so belated that 

 the opening of their flowers had 

 to be delayed over winter. During 

 the dry, windy days of spring, when 

 the farmer sows hi 5 seed-corn, the 

 flowers of our anemophilous trees 

 are in perfection. At this early period, when so few insects 

 are abroad, these unattractive blossoms are not likely to be 

 favoured with their visits. 



A marked peculiarity of anemophilous trees is the 

 appearance of the flowers before the foliage ; the blossoms 

 of the elm, poplar, ash and willow, for example, are put 

 forth whfle as yet the branches are entirely leafless. This 

 arrangement is clearly advantageous ; the foliage would 

 protect the flowers from the wind, preventing it from 

 gaining access to the stigmas and interfering with the 

 removal of the pollen. 



The fir does not shed its leaves in autumn as deciduous 

 trees do, but its needle-like foliage interferes as little as 

 possible in the way indicated ; nevertheless, the male and 

 female cones are developed ou the branches of the fir iu 

 the most exposed positions. A good illustration of the 



manner in which wind-fertilized 

 plants secure the exposure 

 of their blossoms is seen in 

 the dog's-mercury {Mercuriulis 

 pcrenniii). This plant, com- 

 mon in most districts, has 

 rather large leaves ; they ex- 

 pand before the flowers, and 

 would be a great hindrance 

 to wind-fertilization were it 

 not that the little staminate flowers are elevated on long, 

 slender stalks which spring from the axils of the leaves and 

 entirely overtop the foliage. The male catkin of the oak 



Fig. 4. — Inflorescence of 

 the Quaking Grass. 



Fig. 5. — Unisexual Flowers 

 of Nettle. 



