224 



HA RD WICKE 1 S SCIENCE- G OSSIF. 



which forms a ledge reaching along the humerus to 

 the elbow, and'thence to the junction of the ulna and 

 radius with the bones of the wrist, being greatest at 

 the elbow. In the soaring birds this ledge is largely 

 developed, projecting downwards in the frigate birds 

 one and a-half inches at the elbow, tapering to the 

 wrist and body. This ledge, at the front edge of the 

 wing, seems at first view to be an obstruction to 

 flight, as it makes considerable thickness where the 

 surface first meets the air, but, as we shall presently 

 see, has an important function to perform as a member 

 of the organised mechanism of flight. The curves in 

 the plane of the wing need not be considered as they 

 are not concerned with flight, and when the bird is in 

 the act of flying they are straightened out so that the 

 wing assumes a plane shape. The above four peculi- 

 arities we desire to note. Firstly, that the wing is 

 practically a thin plane. Secondly, that its rear edge 

 is very pliable and elastic. Thirdly, that its under- 

 surface is rough to 'motion from rear to front, but 

 smooth to motion from front to rear. Fourthly, that 

 it is supplied with a ledge along its under-surface at 

 the front. 



{To be continued.) 



STUDIES ON COMMON TLANTS. 



No. VI. — The Musk {Mimulus). 



By E. A. Swan, B.A. 



THIS is a very good example of the persistence of 

 a type with such amount of variation as may 

 from time to time be beneficial, such variation, how- 

 ever, being confined within certain well-defined 

 limits, the expression here not being used in the 

 strict Darwinian sense. In saying this, I have in 

 view more especially the rhizome, or underground 

 creeping stem, which, as can be seen by reference to 

 Fig. 145, is characterised by great versatility ; thus, if 

 roots are expedient, it throws out roots abundantly at 

 the nodes ; if branch stems, then let there be branch 

 stems ; if both, then both are produced. Moreover, 

 the end of the stem generally withers, and this is 

 probably due to its having sufficiently sapped the 

 earth in that quarter, and rendered any farther ex- 

 penditure there unnecessary. But sometimes branch 

 stems, as well as the main stem, rise above-ground, 

 and these are often supported by aerial roots from the 

 first node. Again, there are rudimentary buds below 

 ground, and real buds and leaves above ground, 

 while in place of the roots at the nodes, we have all 

 over the stem, above ground, fine hairs ; we have too 

 the flowers. The development and growth below 

 keep pace with the development and growth above. 

 A good floral display being required for the purposes 

 of reproduction, the underground mining operations 

 are carried on in different directions to secure the 



constant demand for sap. In the figure it will be 

 noticed that one branch stem rises upwards, while 

 its mate from the same node humbly prefers to carry 

 on root work ; this admirably illustrates the unanimity 

 that exists between all parts of the plant to contribute, 

 in one way or another, useful assistance and to avoid 

 waste. The influences that induce these two branch 

 stems to act as they do, may be difficult to guess, 

 for, at the first glance, there appears to be no tangible 

 reason why they should not both act alike. But a 

 solution of the problem may be found in the assump- 

 tion, that the particular direction of any stem depends, 

 in the first place, on the richness or comparative rich- 

 ness of the soil at any one spot ; and where, from its 

 position, one branch stem has the advantage over 

 another, that other may elect to grow upwards. 

 True this is only a guess, but in considering the 

 subject, the law of necessity which plays such an im- 

 portant part in vegetable life, must not be lost sight 

 of. That law, in its working, tends to preserve the 



balance between supply and demand, and it is always 

 exercising its power, not only on the whole plant 

 generally, but on each cell and each minute part 

 particularly, so that a branch stem in its inception, is 

 subject to and governed by it. If one stem, from the 

 accident of its position or from other causes, devotes 

 itself to collecting sap, another stem less favoured, 

 must direct its attention to an equally necessary task, 

 viz. carbon producing, and for that purpose seek the 

 light. They each grow necessarily in the direction 

 where they will be of most service, and where they 

 can most readily obtain supplies. By a kind of 

 natural selection, one stem, from its inherent strength 

 or character, or from its location, being most fitted to 

 collect sap, leaves nothing in that way for the other, 

 which must therefore wither and die, or search for a 

 fresh sphere of usefulness. 



I will now devote a short space to the consideration 

 of the flower. Passing from the calyx, upon which 1 

 make no comment, I take the monopetalous five-lobed 

 corolla ; looked at from above, it presents the shape 



