March 2, 1891.] 



KNOWLEDGE 



63 



the seed or kernel. Where the seed is so protected, it 

 may itself be comparatively soft. The pomegranate and 

 gooseberry are exceptional in this respect, that the testa, 

 or outer layer of the seed, is developed in a succulent 

 manner, the central core of the seed being, however, hard. 

 The strawberry has the top of the flower-stalk very much 

 enlarged ; the edible portion is, in fact, formed from the 

 thalamus (or spreading portion of the stalk from which 

 the flower springs), the fruits being the little yellow seed- 

 like bodies studded over its surface. The raspberry and 

 bramble, on the other hand, have a dry, conical thalamus, 

 on which are arranged a number of drupes corresponding 

 in structure to the plum and cherry. In the mulberry the 

 succulent portion is furnished by the calyx, and in the 

 apple and fig the hollow receptacle, or flower-stalk, supplies 

 the food material. From the small size of the seeds of 

 berries we may infer that they are adapted to be swallowed 

 along with the pulp. In the larger drupes the size of the 

 stones and their rough or jaggy exteriors, as seen in the 

 peach-stone, seem to indicate that the intention here is to 

 induce the bu'd to fly to a distance with the fruit, and 

 after devouring the soft portion, to drop the hard endocarp 

 containing the seed. Where a fruit is not intended to be 

 eaten it invariably acquires a hard and dry character. 



Fruits adapted to birds are for the most part sweetly 

 tasted. They contam, in addition to sugar, organic acids 

 and essential oils, which confer an agreeable or even 

 delicious flavour to the fruit, and constitute an attraction 

 to birds as powerful as the nectar of flowers is to insects. 

 If these quaUties appeared too soon there would be a 

 danger of the seeds being removed before they were ripe. 

 Accordingly the fruit remains sour until the seeds are 

 matured. 



Succulent fruits are brightly coloured, to be easily 

 recognised from a distance. Conspicuousness may be 

 increased, as in the clusters of the grape, rowan, and elder- 

 berry, by the massing together of the single fruits in 

 groups, just as happens in composite and other flowers 

 where the florets are crowded on a contracted inflorescence. 

 The colour of the fruit in general presents a strong con- 

 trast to the foliage. If the fruit remain on the tree after 

 its leaves have fallen, its colour will challenge attention all 

 the more as the season advances. The scarlet fruits of 

 the wild rose thus remain on the bare branches and pre- 

 sent a most conspicuous appearance. When the ground is 

 covered with snow, coloured berries form prominent objects 

 in the country landscape. Artists frequently avail them- 

 selves of this contrast, and introduce into snow scenes a 

 sprig of holly with its scarlet berries. When Zeuxis 

 painted the picture that deceived the birds, he may have 

 taken advantage of this contrast ; but perhaps it was left 

 for Father Christmas to reveal to us how perfectly the 

 colours of fruits serve the purpose intended by nature. 



The list of plants bearing coloured fruits includes the 

 following, which are British : — berberry, bittersweet, 

 spindle-tree, strawberry, rose, hawthorn, currant, rowan, 

 dogwood, honeysuckle, whortleberry, cranberry, bearberry, 

 holly, daphne, arum, asparagus, lily of the valley, yew, 

 alder, sloe, bramble, elder, bilberry, crowberry, juniper, 

 misletoe, and snowberry ; besides these, may be mentioned 

 the orange, tomato, fig, date, olive, and mango. The 

 colours of fruits arc less varied than those of flowers. 

 Possibly this may arise from the circumstance that wliile 

 it is of importance, as regards fertilisation, that insects 

 should be able to recognise and distinguish dirtereut species 

 of flowers, there is no necessity for birds to distinguish 

 difl'erent fruits, or to conliue themselves to one kind of fruit, 

 as insects restrict themselves for a time to one species of 

 flower. Although never variegated like flowers, nuinv fruits 



under cultivation exhibit a twofold colouration ; thus we 

 have red and green gooseberries, purple and green grapes, 

 red and white strawberries and currants, green and purple 

 plums, &c. 



[To he contimu'd.) 



VARIABLE STARS OF THE ALGOL TYPE. 



By Miss A. M. Clerke, AiUlivr of ".1 Popular History 

 oj A.itronoini/ durini/ the Xinett-'ent/i Century" and 

 " Tlw System of the Stars." 



TEN stars of the Algol type are now known — ten 

 stars, that is to say, which vary in light not so 

 much physically as geometrically, through the 

 accident of our point of view. They are, to begin 

 with, very rapid binaries ; but other binaries 

 equally rapid shine with sensible constancy. It is only 

 when the orbits of the revolving stars lie so nearly edge- 

 wise to the earth as to involve mutual occultations, that 

 the peculiarity of a sudden loss of light at brief intervals 

 is added to the peculiarity of composition into abnormaUy 

 close systems. This has been spectroscopically demon- 

 strated as regards Algol ; and the other members of the 

 class copy its phases with such fidelity as to leave no doubt 

 that they too are genuine " eclipse stars." To argue the 

 point would be to enfoneer une porte ourertc. 



But this is not all. There are residual phenomena not 

 amenable to explanation, simply by the recurring transits 

 of a semi-obscure mass. Eclipses beyond question in all 

 cases occur, and produce their due efi'ects ; yet compUcated 

 with others owning a different origin. Slight as these 

 often are, their investigation offers perhaps the most 

 promising clue to the labyrinth of stellar ///ii/.v/(V(/ varia- 

 bility. For their evident connection with certain calculable 

 phenomena of eclipse defines clearly the conditions under 

 which they occur, and strongly suggests their origin 

 through some form of mutual influence by closely re- 

 vohing bodies, demonstrably of low average density. More- 

 over, the residual variations of Algol stars are of a 

 nature tending to bridge the gap separating them fi-om 

 other variables. That is to say, the irregularities of 

 light-change in the two orders show a very ciuious 

 inverted correspondence, as if the same causes which 

 produce darkening in the one set of objects produce 

 brightening in the other. This unlooked-for circumstance 

 can scarcely fail to become the guide to some important 

 truth. 



For eliciting it, however, observations both more de- 

 tailed and better assured than those yet obtained are 

 urgently needed ; and it seems unhkely that they will be 

 available until in this, as ah'eady in so many other de- 

 partments of astronomy, the retina is superseded by the 

 sensitive plate. The eye is nowhere more subject to 

 illusion than in following the course of rapid liuninous 

 fluctuations ; and its disabilities are not removed by any 

 kind of auxiliary apparatus. Its very powers of adapta- 

 tion, indispensable to it as a living organ, serve to impair 

 its usefulness as a photometer. The stars, then, must 

 register their own changes, and the method of photo- 

 graphic trails appears eminently suitable for the purpose of 

 inducing them to do so. Professor Pickering has shown 

 that comparative measures of different stars made in this 

 way are reliable to about one-tenth of a magnitude ; and 

 discriminations based upon the varying width and in- 

 tensity of successive sections of the same trail might be 

 expected to reach a still higher grade of precision. Some 

 practical ditliculties would certainly have to be met, but 

 probably none that would prove insuperable. Thus, an 

 arrangemoiit might be contrived lor automatically, at fixed 



