August 1, 1891.] 



KNOWLEDGE 



149 



In the manufacture of chsese the nitrogenous material 

 of milk (caseine) is thrown out of solution in the solid 

 form by the action of rennH (an infusion from the stomach 

 of the calf), whilst the greater part of the milk sugar 

 remains in solution in the whey. Cheese contains also 

 inorganic matter and a variable proportion of fat. A large 

 proportion of fat imparts richness to cheese, the richest 

 cheeses, such as Stilton, being made from milk with added 

 cream. There are also cheeses made from ordinary milk, 

 or " whole milk " cheeses, and cheaper kinds made from 

 skim milk. In these diflferent varieties the proportion of 

 fat varies from 20 to more than 40 per cent., the propor- 

 tions of caseine and of water having about the same range. 

 It sometimes happens that margarine fats are used in 

 making cheese, as an economical method of imparting 

 " richness." The detection of the fraud may be made by 

 separating the fat and subjecting it to the same tests as in 

 the- analysis of margarine. 



ON THE FERTILIZATION OF TWO COMMON 

 BRITISH ORCHIDS. 



By -J. Pentlaxd Siiith, M.A., B.Sc, &c.. Lecturer on 

 Botany, Horticultural College, Swanley. 



FOE some years Orchids have been in high favour 

 with iiorists and that section of the flower-loving 

 public who can indulge in the luxury of a hot- 

 house. Most of the quauit and beautiful specimens 

 one sees have their home in the tropics, and are 

 epiphytes (that is, they obtain the whole of their food from 

 the au-). We will content ourselves with the examination 

 of two plebeian members of the family that are to be found 

 in plenty in England, and are of terrestrial growth. They 

 are quite as interesting as their exotic brethren. The 

 first of these, the early purple Orchis (Orchis inuscida), 

 a month ago was flowering in our woods. The first 

 thing that strikes the casual observer on examining these 

 Orchid flowers is the curious shapes they assume, a cir- 

 cumstance that has led to the application to them of such 

 names as Butterfly Orchid, Frog Orchid, and Bee Orchid, 

 these names indicating their supposed resemblances to h%ang 

 creatures. The appearance of the early purple Orchis is 

 no less striking. This name has been applied to it on 

 account of the reddish-purple flowers that make their first 

 appearance during the month of April. It continues 

 flowering until July, its flowers ai-e grouped in spikes, and 

 are occasionally almost white. They arise fi-om the axil 

 of a coloured bract. 



In plants with net-veined fohage leaves, the outer 

 covering of the flowei- — the crily.v — is composed, as a rule, 

 of green-coloured modified leaves (si-palu). But tlie Orchid 

 ranks amongst the ^lonocotyledons — plants with parallel 

 veined foliage leaves, and coloured sepals— which are thus 

 often indistinguishable from the inner whorl of enveloping 

 organs (the jntals). Fixing our attention on a single flower, 

 and holding the spike so as to bring the flower next us 

 and the stalk or /i.n'x from which it springs away from us, 

 we notice that one of the throe sepals lies next the axis, 

 and is consequently further away from the body of the 

 spectator than the other parts of the flower, and is 

 superior in position to these ; it is thus said to be posterior 

 or superior, while the other two are termed the lateral 

 sepals. Alternating in position with these organs are 

 three petals. Th(i two lateral ones are of small size ; the 

 third, or odd one, is anterior or inferior in position, and 

 is abnormally developed into a broad, expanded, purple- 

 spotted lip, or three lobes. The middle lobe is longer 



than the others and is notched at the tip. This petal is 

 termed the lahellum (Fig. I. 1). An opening near its point 



-JoUcK rr^a.fSi$ 



vc^lell'"-"*- 



Fig. I. — 1. Semi-diagi'ammatie riew of the flower of OrchU 

 maculata, magnified (which agrees practically in sti-ucture and in 

 method of fertilization mth Orchis mascula). The ovarv is made to 

 shine through the bract ; the labellum is cut through the middle, and 

 the left anther-lobe is also seen m section. The left petal is 

 removed. 



2. Front view of stamen and rostellimi. 



3. Group of pollen-masses. 



of origin leads into the canal of a stout pouch or spur, 

 with which it is furnished. Situated opposite the posterior 

 sepal there is a shield- shaped body, at whose base is a 

 small bulbous swelling, the rostelluiK (Fig. I., 1, 2). The 

 latter more or less obstructs the entrance to the pouch of 

 the labellum which it overhangs. The sides of the shield 

 are swollen; the swollen portions (Fig. I., 2) narrow as 

 they approach the rosteUum, and each one is slit from top 

 to bottom. A closer examination of these will amply 

 repay us for the time so spent. First, then, we will take 

 a fully-expanded flower, and insert the end of a well- 

 sharpened lead-pencil into the spur of the anterior petal. 

 If withdrawn immediately, two small Indian club-shaped 

 bodies (Fig. I., 1) will probably be found adhering to it. 

 We say " probably," because these bodies may have been 

 removed already. They are simply masses of poUen 

 (Fig. I., 3) held together by elastic threads. The union 

 of the threads forms the handle of the club, and is called 

 the raiiiliil:' or little stalk ; the caudicle rests on a smaU 

 plate of tissue termed the dixf. The whole structure is 

 called a imllinium. Further examination of the swellings 

 of the shield shows that their cavities are now empty ; the 

 poUinia formerly occupied them. 



In an ordinary flower, the pollen grains are contained 

 in two lobes at the summit of the stamens, caUed the 

 anther-lobes. Wlien these open the pollen grains fall out 

 as a fine powder, as they are more or less free from one 

 another, but in Orchids the contents of each anther ai-e 

 shed en nwsxc in tlie shape of the pollinia described above. 

 Each swelling of the shield is thus an anther-lobe, and the 

 whole shield is a xUaiien. The tissue between the lobes is 

 the connective, the upper portion of the stalk or filament 

 of tlie stamen. The great separation of the lobes from 

 one another is not unique. It is frequent in other kinds 



