September 1, 1899.] 



KNOWLEDGE. 



211 



latifolia, remarkable as being visited almost exclusively 

 by wasps. There is no spur, but the concave labellum 

 contains a copious supply of nectar. The square stigma 

 is surmounted by the rather small rostellum ; the pollinia, 

 which have no stalks, are both attached to one disk, and 

 are removed together by visitors very much as in the 

 orchids just described. Orcliis pi/ramidalis also has but 

 one disk ; it is saddle-shaped, and clasps the visitor's 

 proboscis ; the curving of the disk causes the pollen- 

 masses attached to it to diverge, whereby they come more 

 readily in contact with the stigmas of the next flower. 

 Self- fertilization occurs extensively in the fly and beeorchises. 

 A singularly interesting group, the Cypripedinae, is 

 represented in this country by the lady's-slipper orchid, 

 which occurs (unless it has been recently extirpated) in 

 the north of England. Many species of Cypripedium 

 are cultivated for the sake of their flowers, which are 

 much larger than any of our native orchids, though 

 as a rule they are produced singly, and not in clusters 

 or spikes. Cypripedium difl'ers from the common 

 orchid in several respects. The pollen grains are not 

 combined into pollinia ; instead of only one, it has two 

 perfect stamens which belong to the inner whorl, and 

 correspond to the two little swellings at the sides of the 

 fertile stamen of the orchis. The latter is represented in 

 Cypripedium by a large flattened staminode, which partly 



closes the opening of the 

 lower lip. The lip itself is 

 hollowed out into a kind 

 of pouch in front of the 

 flower. Its upper edges are 

 incurved in such a way that 

 an insect cannot escape by 

 the opening through which 

 it entered. The visitor is 

 consequently forced to crawl 

 up inside the labellum, and 

 squeeze itself thi-ough one 

 of the two little holes higher 

 up, where the labellum 

 arises from the column. 

 To reach either of these apertures the visitor must first 

 creep under the stigma. Should there be any pollen on 

 the bee's back this will be transferred to the stigmatic 

 surface. Above each little opening one of the anthers 

 is so placed that the pollen is brushed ofl" by a bee as 

 it makes its escape. This pollen the departing guest 

 will not fail to carry with it when it enters the labellum of 



Cypripedium. Sand 

 miAcT bees have a special 



liking for this flower, 

 and large insects are 

 occasionally found dead 

 in the labellum, from 

 which they have been 

 unable to escape. The 

 flowers are of various 

 colours — shades of 

 white, yellow, crimson, 

 and pink — according to 

 the species, but the 

 prevailing tint is chocolate brown. A species common in 

 America, with large nodding blossoms of pale crimson 

 colour, is known as the mocassin-flower. The genus has 

 recently been re-arranged into a number of sub-genera, 

 and many species have been re-named. 



One of the Australian orchids, Pterostylis longifolia, has 

 a sensitive labellum which acts as a spring trap. 'When 

 an insect alights it instantly flaps up, and the unwary 



F IG. 5. — Cypripedium barbatum. 



Fig. 6.- 



-Seetion through Labellum 

 of Slipper Orchid. 



There is only one 



visitor is entrapped in the flower, 

 opening above by 

 which escape is pos- 

 sible, and, as happens 

 in Cypripedium, the 

 stigma and anther 

 are encountered on 

 the way out. An 

 irritable labellum also 

 occurs in species of 

 Megaclinium, Bolbo- 

 phyllum, Drakea, and 

 others. In the vanilla 

 orchid, the pods of 

 which supply the 

 well-known flavour- 

 ing, an arrangement 

 of hairs, somewhat re- 

 sembling the mouse- 

 trap hairs of the birthwort, induces visitors to enter and 

 depart in the manner most favourable to cross-fertilization. 



Fia. 7. 



-(1) Plerostylis : (2) with 

 Labellum folded. 



ELECTRICITY AS AN EXACT SCIENCE. 



By Howard B. Little. 



V. — Electrical Reasoning and Incontrovertible 

 Electrical Fact. 



SINCE mathematical reasoning and logical truth are 

 the same, all the world over, and in every walk of 

 life, it follows at once that no extraordinary form 

 of reasoning should have been introduced by 

 electrical workers, unless they wished to forfeit 

 their science's claim to be considered exact. A consideration 

 of all electrical laws (and aU legitimate deductions there- 

 from), will render it quite clear that electrical reasoning is, 

 as it should be, no more than the application of the soundest 

 reasoning we know to the immutable laws of the science. 

 Consider the simplest law that occurs at the moment, 

 " The sum of the currents flowing to a point is equal to 

 the sum of the currents flowing from that point." The 

 " casually inclined " student might perhaps smile, and 

 even say " obvious." And there would be a certain 

 amount of excuse for him in this instance (but bear in 

 mind that a simple rule was purposely selected). Apply 

 Euclid's definition of a point, " That which has no parts 

 and no magnitude." Can any change occur in such a 

 position, when the word position does not imply space ? 

 Mathematically, then, it is a statement which may be 

 regarded as an axiom. But the law thus enunciated 

 becomes of real importance when we have to consider that 

 portion of a circuit where one conductor divides into many 

 branches. Here the law of shunts comes in, and we find 

 that the current flowing in each branch or shunt may be 

 represented by a number which is inversely as the resist- 

 ance of that particular branch, or proportional to the 

 conductivity, where this latter quantity is, of course, 

 expressed as the reciprocal of the resistance. 



Once having clearly realised that every electrical 

 quantity is subject to some more or less direct form of 

 measurement, we see that all such quantities may be 

 represented by numbers, these numbers being in their turn 

 regarded as the representatives of so many units. The 

 conception of positive and negative quantities is not so 

 easily arrived at, because we (for some occult reason) 

 adhere to the unfortunate expressions positive potential, 

 and negative potential. These phrases imply to the 

 beginner that there is a difference in quality between the 

 two potentials thus referred to. Nothing of the kind is, 

 however, the case. It has already been pointed out that 



