212 



KNOWLEDGE 



[Reptkmber 1, 1896. 



controllable that, without a directive force, the phenomena 

 seem quite inexplicable. 



Moreover, all my own observations lead me to accept tlie 

 theory of a direct propelling force, and I can hardly accept 

 the couclusions on this point of Mr. Blackwall, though he 

 is an authority on the subject. The intense rapidity with 

 which the initial movements arc made cannot be reconciled 

 with any tlieory of simple atniosplieric convection ; and 

 illustrations such as the following go to prove that spiders 

 possess the faculty of weighting or condensing the ends of 

 their threads, and throwing them, within limited distances, 

 to a point fixed upon. 



1 was writing, and had two shoots of quarto before me. 

 Perceiving a small spider on the paper I rose and went to 

 the window to observe it. To test its power of passing 

 through air, I held another sheet about a foot from that 

 on which the creature was running. It ascended to the 

 edge, and vanished ; but in a moment I saw it landing 

 upon the other sheet through mid-air in a horizontal 

 direction, and picking up the thread as it advanced. 



In this case there was no air-movement to facilitate, nor 

 any time to throw a line upward, which, indeed, would not 

 have solved the difficulty. Propulsion appears the only 

 explanation. 



The next illustration is more marvellous, and seems to 

 indicate that some species, at any rate, have the power of 

 movement through the air in any direction at will. 



Some years ago, at a dinner party in Kent, four candles 

 being lighted on the table, I noticed a thread strung from 

 the tip of one of the lighted candles close to the flame, and 

 attached to another candle about a yard off ; and all the four 

 lights were connected in this way, and that by a web drawn 

 quite tight. No little surprise was caused among the guests 

 on finding that the diamond form of the web was complete. 



No satisfactory explanation of this has been offered, and 

 I can only suggest that the spinner was suspended at first 

 by a vertical line from above, and thus swayed itself to and 

 fro, from tip to tip of the caudles. It was certain that the 

 spider could not have ascended from the table ; and it was 

 equally certain that aerial flotation of the line from a fixed 

 point was impossible, as it involved floating in four opposite 

 directions. I have seen a creature of this or a nearly 

 allied species moving laterally through the air of a room 

 in this way. 



♦ 



THE AFFINITIES OF FLOWERS.-THE 

 HAREBELL AND THE DAISY. 



By Felix Oswald, B.A.Lond. 



FEW subjects are more fascinating to the botanist 

 than the investigation of the natural relationships 

 existing between the various orders of flowering 

 plants. Very often these affinities have become so 

 much obscured by later adaptations which have 

 rendered the flower better suited to dift'erent surroundings 

 that it is not easy to detect, by mere inspection, its more 

 deeply-seated relations. 



For instance, there does not seem, at first sight, to be 

 any resemblance between a harebell and a daisy ; but in 

 this paper the attempt will be made to show, by the 

 study of characteristic intermediate types, that the two 

 flowers, externally so dissimilar, may yet be considered to 

 mark the opposite extremes of one and the same series. 

 Of course it is not intended for one moment to infer that 

 the one is directly derived from the other ; on the contrary, 

 they stand to each other in the relation of distant cousins, 

 very many times removed, the one having retained to a 

 greater extent the features of the common ancestor, while 

 the other has become more highly specialized in quite a 



different direction. Keeping this principle in view, we 

 may regard the flowers which are chosen hero to bridge 

 over tlie gap as indicating roughly the various stages from 

 a lower to a higher type of structure. It must, however, 

 bo remembered that these transition forms — harebell, 

 rampion, sheep's bit, hemp-agrimony, and daisy — have 

 deviated each more or less from the direct line by reason 

 of adaptation to climate and surroundings as well as to the 

 severe competition to secure a place in nature, but most of 

 all to the requirements of those insects which have (by 

 parallel development) become best fitted to cross-fertilize 

 the particular species. 



Everyone is familiar with the delicate drooping blue 

 ilower of the harebell, or witch's thimble — a pale IdIuc so 

 perfect as to seem to be the reflection of the sky. Let us 

 now pluck a flower and examine it more closely. The five 

 teeth on the margin of the bell indicate that it is made up 

 of five petals. The bell, however, is not formed by the 

 mere coalescence of the petals by their edges, but by the 

 intercalary growth of the tissue at their bases raising them 

 up. Thus the teeth or lappets alone represent the petals. 

 The body of the bell, as in most tubular flowers, is a new 

 and superadded structure ; indeed, in some members of 

 the CampanulaceiB or harebell family — c.//., the sheep's bit 

 — the corolla-tube is so short that at first sight the petals 

 appear to be quite separate from each other (Fig. A). 



When we come to examine the 

 really essential parts of the flower, 

 viz., the stamens and pistil, we find 

 that they present a different appear- 

 ance according to the age of each 

 flower. Thus, just before the flower 

 bud has opened, the ripe anthers are 

 closely pressed against the immature 

 cylindrical style. The latter is pro- 

 vided with longitudmal rows of small 

 stiff hairs projecting into the anther- 

 cells, which have opened inwardly, 

 , are "introrse"). Consequently, as 

 the style grows in length, the pollen is swept out of the 

 anthers by these hairs, and is left adhering to the surface 

 of the style in a broad zone. The stamens, having now 

 fulfilled their purpose, shrivel up and wither. This is the 

 state of things which a newly opened flower presents to 

 view. The style continues to grow longer, and finally 



^ 



Fio. A.— Single Horet 

 of Sheep's Bit. 



facing the style {i.e. 



Fio. B. — Section of Harebell at successive stages. I. Stamens 

 depositing pollen on style. II. Stamens shrivelled; stigmas still 

 immature. III. Pollen removed by a bee ; stigmas expanded. 



expands at its apex into three branches, exposing the 

 stigmatic surfaces, which are sticky, in order to catch and 

 retain the pollen-grains brought from another flower.* 

 (Fig. B, I., II., III.) 



A bee visiting a young flower of the harebell will 



* The harebell thus furnishes us with a very clear and instructive 

 example of the phenomenon termed " protandry " — that is to say, the 

 anthers reach maturity anil shed their jiollen before tlic stigmatic 

 surfaces of the same llowcr arc ready to receive the fertilizing grains. 

 By tliis means self-fertilization is avoided, and the llowcr secures, by 

 the agency of winged insects, the advantages arising from being 

 crossed with other flowers of the same species. 



