1322 



PHYSIANTHUS 



PHYSIOLOGY 



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

 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-S% in. across, tinibelUite. 

 Ara&jia gravSolens, Masters ( Phijsidnth us graviolens , 

 Hort. P. uKricfinius, R. Grab. Sclnibertia graveolens, 

 Lindl. i'. gramlifldra. Mart.). Den.sely 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.P. 3:369. G.C. III. 4:271. Gn. 32:607. A. G. 13:695. 



AA. Fls. 1 in. across, cymose. 

 Aradjia seric6fera, Brot. (A. dlbens, G. Don. A. seri- 

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

 dnthiis 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 PhysiantJius albens or Araujia albens of the 

 trade. q -^ Oliver and W. M. 



PHYSIC NUT, FRENCH. Jatropha Curcas. 



PHYSIOLOGY OF PLANTS. What PUint Physiology 

 Means. — Thi- viry fart of cultivating plants presup- 

 poses some kuowli-dire of how the plant lives, i. e., of 

 plant physiology. Tne 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- 

 provement have been regu- 

 lated rather by limitations in 

 /J^*¥% SJ man's knowledge of plant-life 



I !'"«; ■ f\ than by any lack of capacity 



* I ■W'^'-i.. 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 

 jilant physiology as a science. 

 With a knowledge of the inti- 

 mate structure of the plant 

 the experimental method must 

 lie applied both in the field 

 ami ill the laboratory. Neither 

 :ii'tii>ns 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 squas 

 plantlet showinc adhe 

 ence of soil particles. 



1778. Cross-section of rootlet showini; 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. — Koot, 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 variati<ins in the re- 

 quirements of leaf, stem and other jtairs .■oiiiniensurate 

 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 Sespiratioii.-'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 accoiiiplisliiil. There is work in maintaining 

 the rigidity of its strn.-ture, in absorbing food material, 

 in supporting and accuiuj^lishing the various comi'lcx 

 internal processes of assimilation, growtli. and dtvcl- 

 opment. The forcing of its roots tlm.iiu'li tin s"il and 

 rock, and the resistance t3the strt-ss uf w mmN ami nttirr 

 agencies are examples of the eneT-L;v clail> cxim-imIiiI in 

 maintaining itself. In order to accoiTiplish 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 stom- 

 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 diffi- 



