HA RD WICKE 'S S CIENCE - G OS SI P. 



177 



Microscopic dimensions in England and America 

 are usually given in parts of an inch ; Continental 

 observers now generally employ some division of 

 the millimetre, such as 'I, 'OI, "ooi ; the latter is 

 sometimes written thus : 1 /* (/* = 1 millieme) -ooi 

 of an English inch = 25 /* -399. An English inch 

 contains 25 mm. "3995- A millimetre may be 

 roughly estimated as being equal to ^ of an inch. 



Ehrenberg, Kiitzing, and the earlier microscopic 

 observers used fractions of the Paris line, or the ■£? 

 of a Paris inch ; the latter equals 27 mm. "12 ; the 

 Paris line equals 2 mm. '255. Rees gives the Paris 

 line -088815 of an English inch ; the nearest vulgar 

 fraction to this is 2-23rds = 087 12 1, differing by less 

 than I -500th of an inch. Practically the French 

 inch is equal to i T ' ff English inch. 



The scale used by Ehrenberg was i-25th of a Paris 

 line, magnified 300 diameters equalling two Paris 

 inches in length. 



NOTES ON THE RHODODENDRON. 



(~\N Saturday, the 1st of June, on our visit to the 

 ^~*f Rhododendrons, at Cobham Park, my atten- 

 tion was drawn to the form of the flower by a query 

 from one of the party as to how fertilization was 

 brought about, seeing that the stamens and style all 

 pointed upwards, and the style was greatly exserted 

 beyond stamens. I was thus led to pay particular 

 attention to the point ; and, I think, was enabled to 

 arrive at a just solution. 



A very small amount of attention demonstrated 

 quite clearly that the plant is proterandrous, i.e., that 

 the stamens arrive at maturity before the stigma is 

 in a receptive condition ; and that, therefore, although 

 the flowers are bisexual, they are to all intents and 

 purposes unisexual, as the stamens of a given flower 

 cannot fertilize the ovary of the same flower. This 

 might be inferred from the size and showiness of the 

 flower, as such plants, it has been clearly shown, are 

 usually entomophilous, i.e., are fertilized through the 

 agency of insects. We were soon enlightened as to 

 the peculiar fitness of the upturned style and stamens 

 for the purpose of securing cross fertilization by the 

 agency of large honey-loving insects, such as the bee. 

 While examining a cluster of flowers a large bee or 

 bee-like insect was seen to enter a flower ; and, 

 alighting upon the stamens, to apply its long pro- 

 boscis to the upper part of corolla at a point about 

 half-way down the tube. An examination of other 

 flowers showed in every case at this part a large drop 

 of fluid matter resembling dew or rain, but which 

 proved, on tasting, to be honey. 



The modus operandi of fertilization was now patent 

 enough. Large insects, such as the bee, are attracted 

 by the honey ; and, from its position within the tube 



of the corolla on the upper side, and from the form 

 and position of the 7tp-curved stamens, are unable to 

 reach it without, in the male condition of the flower, 

 literally dusting the under-side of the thorax and 

 abdomen with pollen, and without, in the female 

 condition, where the style protrudes beyond the now 

 pollenless stamens, depositing a portion of their trea- 

 sure upon the expanded glutinous stigma. Thus, as 

 they flit from flower to flower, in search of honey 

 for their own benefit alone, do these insects unwit- 

 tingly carry on a work that is absolutely essential to 

 the continuance of the specific life of the Rhodo- 

 dendron. 



We may thus in a general way see and admire the 

 mutual adaptation of insect and flower for each other's 

 good, but a closer examination of the flower will 

 reveal to us many small modifications in the form of 

 corolla, stamens, ovary, &c, which cannot fail to 

 increase our admiration. 



ULftlNUS 



CALYX 



oVARr 

 I IMPERFECTLY 1 CELLED 



Fig.* 119. Ovary 

 of Rhododendron. 



Fig. 118. Pistil of Rhododendron. 



INTERIOR 



Fig. 120. Stamen 

 of Rhododendron. 



HONEY CANAL -1 

 DORSAL RIDGEv^^* A 



Fisr. 122. Cross section of tube of Corolla. 



First, with regard to the colour of 

 the corolla. This is of an almost uni- 

 form tint, varying in different plants, 

 from deep rose-colour to pale pink, or 

 even white. Within the tube, how- 

 ever, on the upper side a number of 

 yellow oblong splashes will be found 

 forming more or less distinct lines, 

 clearly converging upon the drop of d £i^"a?W 

 honey already alluded to. Sir J. Lub- of Stamen (mag.), 

 bock has shown by direct experiment 

 that insects profit by experience, and having once learnt 

 that certain lines or striae lead to their food, use them 

 as guides in their future excursions. Hence, doubtless, 



