Septejidei? I, 1885.] THE TROPICAL AGRICULTURIST. 



i6g 



are called secondary products, and are of no further use 

 to the plant, such as akaloids, reshis, volatile oils, tannin, 

 gums, etc. While the process of metastasis can take 

 place under any circumstances, that of assimilation requires 

 special conditions for its proper fulfilment. These coudilious 

 are — (1) the presence of the green-colouring matter called 

 ohlorophyU; (2) sunlight. Any green part of the plant, 

 therefore, which is exposeil to light is capable of assimilating, 

 or, in other words, of mauufactuiiug starch from the 

 crude materials. The leaves, however, are the organs 

 chiefly devoted to this purpose, their various parts being 

 specially adapted for this. 



The outside of a leaf is covered by a thin layer of 

 cells called the epidermis. This layer contains no chloro- 

 phyll, and, therefore, does not manufacture; it simply 

 acts as a protective, and prevents undue evaporation. 

 The epidermis is prorided with openings called " stomata," 

 for the entrance of the carbon dioxide in the air, the 

 carbon of which the plant assimilates, giving back oxygen 

 — a process to be detailed later ou. Each stoma consists 

 of two crescent-shaped cells called "guard cells." By a 

 peculiar arrangement, which I have no time to detail, 

 these cells separate from one another during sunlight, 

 and come together again in the dark, and thus the stoma 

 opens and closes. These stomata are usu.ally situated ou the 

 under side of the leaf. The middle portion of the leaf 

 consists of cells containing chloropliyll. The cells near 

 the upper surface of the leaf, and consequently nearer 

 the light, have more chlorophyll, are long in shape, 

 and are arranged side by side in rows very suggestive 

 of the title given to them of " palisade cells." The cells 

 below these are arranged more loosely, so as to allow 

 free passage of air, and also the evaporation of water, 

 in order that the inorganic salts necessary for assimil- 

 ation may be more abundantly deposited. These cells 

 are called "spongy parenchyma." 



A closer look will show that the chlorophyll is not 

 diffused throughout the cells, but is arranged in round 

 granules. Each granule consists of a network of protoplasm, 

 in which the green chlorophyll is embedde.l. It is the 

 protoplasm which does the work, the green chlorophyll 

 acting only as a shade to protect it from too intense light. 



It remains for us now to consider briefly the influen'-e 

 of external conditions on plaut Ute. It is well known 

 that plant growth can take place only within certain 

 temperatures. The lowest of these is 'o ' O. (32° F.) at 

 which the water freezes, and the highest is from 40'' to 

 50' C. (about 120° F.) at which temperature the albumen 

 coagulates. Some plants, however, in which the water is 

 protected, can live while the ti-mperaturu is below »he 

 freezing point ; and some bacteria have been seen to live 

 in boiling water, having apparently incoagulable albumen. 



From 20° to 30° U. (".5 F.) is the best temperature for 

 plauts to live in. The auuual rings in wood are a good 

 example of the effect of external conditions. Owing to 

 variations of heat, food, etc., the cambium works at 

 greater pressure towards the end of the year, thus pro- 

 ducing ileuser wood. Any number of riiig.s can be artificially 

 produced in one year by simply tyiug a ligature rnunil 

 tbu stem, and alternately tightening and loosening this 

 ligature. The action of light ou vegetation has already 

 been considered. The effect of gravitation ou a plant 

 is a tendency to grow downwards. To counteract this 

 influence, many contrivances arc present in the stem, 

 8u h as the firmness of the wood, the uniform distribution 

 ofc foliage and branches, climbing appliances such as ten- 

 drils, and, in many water plants, air-bladders, Owing to 

 the great variety of conditions tfl whit-li they are exposed, 

 a| 1 plants possess a certain power of adaptation to their 

 e xternal conditions. 



There are two forces which I have time to allude to 

 on'y very briefly. These are heliotropisui and geotropism, 

 Heliotropism is the force whirh makes the stem grow- 

 upwards; geotropism that »vhich makes the root grow 

 downwards. Light and gravitation combined seem to be 

 the chief causes of these phenomena. But I must refer 

 you for further iiiformation to Darwin's exhaustive work 

 on the subje ct. 



After this short sketch of what is already known on 

 the subject, you will see that a vast deal remains jet 

 to be discovered, mneU of which is of great intereit to 



pharmacists, and Wie discovery of which might with advant- 

 age be undertaken by pharmacists themselves. 



Almost uothing, for example, is as yet known about 

 the formation of alkaloids; whether they are really 

 useful to the plant or merely accidental, can only be 

 conjectured. 



It is known from experience that plants possess more 

 therapeutic activity at certain .periods of their growth 

 but the discovery of a scientific law, which would enable' 

 the cultivators of medicinal plants to bring these plants 

 to the greatest perfection remains yet to be made. 



This is only one of the many as yet unsolved proijiems 

 the working out of which would form an interesting and' 

 profitable study, and would prove that botany, however 

 much it has been condemned for its predominance of 

 hard names, is one of the most interesting departments 

 of natural science.— Fluu-nmcciitical Journal. 



A MOTH INJURING DRIED COCOA BEANS. 



In the month of October last I received from the 

 proprietors ot a warehouse at the East-end of London a 

 box contaiuiug a rjuantity of Oocoa beans, which had been 

 found to have been exieusively gnawed all over the outer 

 surface by the larvre of a small moth, together with some 

 of the grubs, some cocoons all matted together, and some 

 of the moths produced from them; and again, at the 

 beginning of December last. Miss E. Ormerod sent me a 

 quantity of these Oocoa beans similarly infested, which 

 she had received from Guyaquil. 



The appearance of the sound Oocoa bean is shown 

 in the upper right-hand figure in the accompany engraving » 

 whilst one much gnawed by the larv.-e is represented 

 in the left-hand upper figure, which shows a quantity 

 of the pellets of the excrement of the larv;e partially 

 detached from the bean. 



The caterpillar, of the natural size and magnified, is 

 represented in the middle of the woodcut; it is long, 

 slender, aud very active, wriggliug about and running 

 quickly either forwards or backwards ; it has six anterior, 

 eight ventral, and two anal claspers ; it is of a dirty flesh- 

 coloured grey, with the head darker and fibrous brown, 

 with a patch of the same colour ou the first segment be- 

 hind the head, in which patch the hind portion forms 

 two darker spots; all down the back are two rows of 

 minute black dots, each segment bearing two on each 

 side of the middle dorsal line, and a third more lateral 

 dot formiug a triangle with the two dor,«al ones. These 

 dots are setigerous ; the penultimate segment of the body 

 has one large central and two smaller lateral black spots, 

 ard the terminal segment has a transverse black spot 

 (the anteuniB in front of the head of the ]arv;e are 

 represented too long aud prominent in the accompanying 

 engraving, aud the caterpillar itself is too robust). The 

 chrysalis is of a chestnut shining colour, and is enclosed 

 in a loose silken web, forming with the other cocoons 

 attached to the Cocoa beans a matted mass. 



The moth measures about two-thirds of an inch in the 

 expanse of the fore-wings, which are of a pale grey colour, 

 with a faint ocbreous tinge, especially towards the inner 

 margin, and with very iudistiuct but darker greyish mark- 

 ings, forming irregular" bars across the fore-wings. Tho 

 first towards the base of the wings is preceded by a 

 pale band, and the second beyonil the middle is grey, 

 followed by a iiale band ; between Ihese bars are two 

 small ones in the middle towards the cost a. On submit- 

 ting the moths to Mr. H. T. Stoiuton. our great authority 

 on the tiny or Tinea moths, he informs me that they 

 belong to the family ot the Knot-horns (rhvd<les), and 

 are the Ephestia i-hitella (I'hvcita elutilla, ' Curtis atid 

 Stephens;, or the cinereous Knot-horn of Haworth. Ho 

 believes that the whole of the species ot the genus 

 Ephestia have similar habits, and devour all sorts of 

 dried fruits, the hirvse being often found in Ra-sins ami 

 Figs, and they are fxtremely partial to all preparations 

 of chocohite, flying by scores in wan-houses where such 

 things are stored. Mr. Staintou, moreover, believes tha-t 

 in a wild state they feed upon Ivy berries and nuts, In 

 an ecouoraical j.oint of view they are noxious insects, 

 aud they cannot certainly he called beautiful. One of 



» Sorry we cauuot reproduce.-rBo, 



