1322 



PHYSIANTHUS 



PHYSIOLOGY 



5 scales attached to the middle of the tube or lower, flat 

 and erect or convex and appressed to the staminal tube : 

 seeds long, bearded. Schubertia and Physianthus should 

 perhaps be considered as subgenera, the former contain- 

 ing the hairy plants with somewhat funnel-shaped fls. ; 

 the latter nearly glabrous plants with somewhat salver- 

 shaped fls. 



A. Fls. 2-2% in. across, umbellate. 

 Araujia graveolens, Masters (Physidnthus graveolens, 

 Hort. P. auricomus, R. Grah. Schubertia graveolens, 

 Lindl. S. grandifldra, Mart.). Densely covered with 

 harsh, spreading yellow hairs : Ivs. 3-4% x 2-2% in., 

 obovate, acuminate, greatly narrowed and cordate at the 

 base, hairy on both sides: fls. funnel-shaped, i. e., 

 swelled at the throat. S.Brazil. B.M.3891. B.R. 32:21. 

 G.F. 3:369. G.C. III. 4:271. Gn. 32:607. A.G. 13:695. 



AA. Fls. 1 in. across, cymose. 



Araujia sericdfera, Brot. ( A. dlbens, G. Don. A. seri- 

 cifera, Ind. Kew. Araujia sericdfera, Mottet. Physi- 

 dnthus dlbens, Mart. ) . Nearly glabrous : Ivs. 3 x 1% in., 

 oblong-acuminate, wide and square at the base, minutely 

 pubescent below: fls. salver-shaped, i. e., not swelled at 

 the throat, pale rose in the bud and only faintly odorous. 

 S. Brazil. B.M. 3201. B.R. 21: 1759. G.C. III. 2:653; 

 20:523. R.H. 1857, p. 89; 1883, p. 488. Gn. 24, p. 409; 

 34, p. 397. Mn. 6, p. 206. The plant as above described 

 is the Physianthus albens or Araujia albens of the 

 trade - G. W. OLIVER and W. M. 



PHYSIC NUT, FRENCH. Jatropha Curcas. 



PHYSIOLOGY OF PLANTS. What Plant Physiology 

 Means. The very fact of cultivating plants presup- 

 poses some knowledge of how the plant lives, i. e., of 

 plant physiology. The pristine cultivator sought to 

 imitate nature, and by a system of selection and in 

 favoring by cultivation the few plants which seemed 

 best suited to his wants, he really improved and devel- 

 oped what he demanded for 

 use. Thus with but little 

 knowledge of how the plant 

 lives, improvement in definite 

 directions has gone forward 

 from the earliest times. Never- 

 theless, the limitations in im- 

 Krovement have been regu- 

 ited rather by limitations in 

 man's knowledge of plant-life 

 than by any lack of capacity 

 for development in the plant 

 itself. Every new discovery 

 in plant physiology must 

 eventually be of value to the 

 horticulturist in one way or 

 another, and the fundamentals 

 of physiology are of prime im- 

 portance. 



A study of plant-life in field 

 and garden alone would hardly 

 have given foundation for 

 plant physiology as a science. 

 With a knowledge of the inti- 

 mate structure of the plant 

 the experimental method must 

 be applied both in the field 

 and in the laboratory. Neither 

 actions nor processes can be 

 intimately known unless the 

 separate activities are in some 

 way isolated and each for it- 

 self investigated by a study 

 of cause and effect. From the 

 germination of the seed, and 

 the interesting changes which 

 this involves, through all of 

 the intricate living processes 

 of breathing, taking in of food, digestion and assimila- 

 tion of food material, and the formation of new plant 

 substance, we have the plant living, the plant in ac- 

 tion. Similarly, as a sensitive organism, it is to be 

 studied as acted upon by all of the external conditions 

 about it, and as responsive to every change of environ- 



ment. In the broader sense of the term, physiology is a 

 study of this living, sensitive, adaptable, reproductive 

 plant. 



Every living process and every change produced by 

 season or other condition has its charm and interest if 

 the underlying principles are understood. A knowledge 



1777. 



Root system of s quash 

 plantlet showing adher- 

 ence of soil particles. 



1778. Cross-section of rootlet showing root-hairs. 



of these broadens the sympathies for the general ob- 

 server of plants and gives the reflective cultivator a 

 truer appreciation of the buoyant living organism with 

 which he deals. 



The Functions of Organs Differ. "Root, stem, leaf 

 and flower are definite organs or parts of the common 

 cultivated plant, and as distinct organs each of these 

 has definite physiological functions, more or less pecu- 

 liar to itself. The root of the soil, bog, water, or epi- 

 phytic plant has in each case peculiarities and modifica- 

 tions of structure, permitting it to do best the slightly 

 differing functions which each is called upon to per- 

 form. In the same way there are variations in the re- 

 quirements of leaf, stem and other parts commensurate 

 with the conditions of growth and the functions of the 

 parts in their relations to external conditions. 



Desert vegetation consists generally of very curiously 

 modified plants. There are, in general, wonderfully 

 thickened and reduced green stems. Many of these plants 

 may store up large quantities of food in their stems, 

 and in some a large supply of water may be stored to 

 tide the plant over long periods of drought. Except 

 in the novel interest afforded, these modifications are 

 more or less meaningless unless it is remembered that 

 here physiological conditions have been seriously modi- 

 fied, and the plants have met their needs in the most 

 serious way. As compared with other vegetation, struct- 

 ure has here been violently subordinated to function. 



Oxygen Supply and Respiration. Even the plant of 

 ordinary culture is not such a dependent organism as 

 its lack of general locomotion would imply. It lives, 

 moves and works every day. In every living process 

 work is accomplished. There is work in maintaining 

 the rigidity of its structure, in absorbing food material, 

 in supporting and accomplishing the various complex 

 internal processes of assimilation, growth, and devel- 

 opment. The forcing of its roots through the soil and 

 rock, and the resistance tathe stress of winds and other 

 agencies are examples of the energy daily expended in 

 maintaining itself. In order to accomplish this work, 

 oxygen is necessary, as with the animal, the energy be- 

 ing secured from the breaking down of organic com- 

 pounds. Ordinarily, the leaf and stem are bathed in 

 the atmosphere, and so the superficial presence of oxy- 

 gen is always assured. By the leaves and green stems 

 oxygen is absorbed mainly through pores (called storn- 

 ates, or stomata) in the epidermis. The stem may also 

 secure a further supply through certain corky cushions 

 known as lenticels, found abundantly in sumac, walnut, 

 elder, etc. Roots also require a constant supply of oxy- 

 gen, and terrestrial or soil roots suffer greatly if de- 

 prived of it for short periods of time. A field of Indian 

 corn flooded with water will soon present a very un- 

 healthy appearance, on account of the fact that water 

 forces the air out of the soil. Cultivation is in part 

 a means of aerating the roots. Many greenhouse dim- 



