GKOWTH. 317 GRUBB. . the ventral side. SimiUir variations in growth are induced by the action of external agents; thus, epinasty i)roduced by the action of the light is designated pholo-epinasty, etc. Nutation is exhibited by yuung leaves of ferns, which are rolled upon themselves in a coil and straighten as they grow older; by the leaves of buds and flowers, whose closed form (bud) is due to the more rapid growtli of the outer faces .■xnd their 'opening' to the more rapid growth of the inner faces. The rate of enlargement is affected in various ways by external stinuili (see Irrita- bility), which 'will be considered later. Ex- amples of very rai)id growth are furnished by the filaments of the stamens of wheat, which elongate, as the flower opens, at the rate of 1.8 millimeters (0.07 inch) per minute (about the speed of the minute-hand of a man's watch) ; by the leafsheath of the banana, which grows at the rate of 1.1 millimeters (.04 inch) per minute; by the flower-axis of the century-plant, which grows at the rate of 1.5 centimeters (G inches) in twenty-four hours : and by the leaves of T"ic- toria regia, which increase in diameter at the rate of .30 centimeters (12 inches) in twenty- four hours. The rate of growtli is studied by means of the auxanometer (q.v.). Internal Development. 'The third phase of growth is the phase of internal development. No increase in size occurs during this phase. It is marked by increase in thickness of the cell- walls (unequal in different parts), by the death of some cells, and by other less noticeable changes. Since the growth ' of different groups of cells (tissues) is rarely eqvial, it follows that the tissues — some compressed, some stretched — firm- ly united as they are, finally exert strains upon o'ne another in various directions, which serve an important purpose in maintaining the rigid- ity of the plant. "Factor.s on Which Growth is Dependent. The conditions of growth are four: First, an adequate supply of constructive materials, which are necessary for the formation of a new organic substance, protoplasm, cell-wall, etc. ; second, an adequate supply of water, which is necessary for the enlargement of the cells; third, access ■ of free oxygen, which is necessary for respira- tion, by which the requisite energj' is set free; fourth, a temperature within definite limits, which, however, vary with different plants, the minimum being approximately 0° C. (32° F.),and the maximum '40° C. (104° F.). The best aver- aae tem])cr.iture foi- the growth of most of the higher plants lies between 25° and 32° C. (77° and 89.0° F.). The effects of external agents upon growth are numerous and profound. Scarcely any change in external conditions can occur without modify- ing the growth nf the plant. These effects may be unequal in different tissues, or in different parts of an organ, or they may be uniform, so that the total growth of the part is retarded or accelerated. The most noticeable effects, natural- ly, are those which produce curvature and conse- quent displacement of certain parts. See under C'HEMOTROPISM; ElECTROTROPISM ; GeOTROPISM IN Plants; Heliotropism ; Hydrotropism; Kheotropism ; Thermotropism ; and Tiiigmot- BOPISM. The most important effects upon the general rate of growth are those produced by temperature and liffht. In general, growth is ac- celerated by increased temperature up to the op- timum point, but further increase beyond the optimum retards it. On the other hand, growth seems to be delinitely retarded by light. Since under ordinary conditions plants are subject to daily variations in temperature and light, thcii,- arises a corresponding daily variation or 'daily period' in the rate of growth ( Fig. G) . Since the temperature rises during the day and diminishes during the night, the general effect will be to accelerate growth during the day and retard it during the night. As light, however, retards gruwth during the day, the final effect will be a resultant between these two opposing factors, the effect of light as a rule predominating. The min- imum usually occurs in the afternoon and the niaximum after midnight, and this variation per- sists for many days, if plants be kept in contin- uous darkness. Correlation, The growth of one part of the plant is directly affected by the activity of an- other. Thus the failure of a certain organ to develop may determine the development of an- other to an unusual extent or in an unusual form. This mutual influence of jilant organs, both as to their formation and the course of their development, is termed correlation. Ex- amples of correlation may be found in the de- velopment of the stipules of the pea and the pansy to an extraordinary size when the leaf- blades are removed early ; in the continued blos- soming of plants when fruit is not pennitted to form;" in the symmetrical or grotesque shaping of a plant made possible by pruning; in the transformation of an underground branch of the potato, which would normally form a potato at its tip, into an aerial shoot bearing leaves and flowers when the aerial parts are cut away. GRUB (connected with OHG. grubilon, Ger, griibbcln, to dig, and Goth., OHG. graban. Ger. graben, AS. grafan, Eng. grave). The name com- monly given to the larva of a coleopterous in- sect." Thus the larva^ of the Slay beetles of the genus Lachnosterna, found commonly in the soil, are known as 'white grubs.' The larvae of certain (lies (Diptera) are also called grubs, although the term 'maggot' is now specifically applied to them. Thus 'grubby cattle' means, in the West, cattle affected by the. 'ox-bot' or 'ox-warble,' the larva of the dipterous insect Hiipoderma lineata. The 'erub' of sheep is also the larva of a fly {(Estrtis oris). See Beetm; Bot; Wabble-Fly. GRTJBB, Sir Howard (1844—). An Irish astrcmomer and instrument-maker. He was born in Dublin, Ireland, July 28, 1844, being the son of Thomas Grubb (q.v.), the famous optician, whose business he succeeded to in 1868. He was educated at Trinity College, Dublin. Under his direction the optical establishment founded by his father achieved increased reputation, and constructed a large number of telescopes, includ- ing those for the I'niversity of Oxford and the observatory at Potsdam. Sir Howard Grubb was knighted in 1SS7. He was vice-president of the Royal Society of Dublin, honorary secretary of the Royal Dublin Society, president of the Photographic Society of Ireland, and a member of the Board of Irish Lights Commissioners. GRTTBB, Thomas (1800-78). A distinguished Irisli optician. He was born at Kilkenny, Ire- land, and in the course of his life constructed the equipment of some of the most important astro-
