234 THE NA TURE- S TUBY RE VIE W [3 : 8-nov. , 1907 



4. Remaining topics (respiration, etc.) noted under animals apply- 

 to plants. 



5. Plants, not green, nourished largely by organic foods. 



6. Insectivorous plants capture insects, etc., for food, apparently. 



Self -protection. Not active opposition or flight as in many ani- 

 mals, but passive defense against, 



1 . Attacks of animals or other plants. Met by 

 — Distasteful or poisonous substances. 



— Armor (prickles, spines, thorns, hairs, etc.), 



— Mimicry, possibly in a few. 



— Utilization of allies such as insects, etc. 



2 . Too much or too little water. 



3 . Too much or too little light . 



4. Extremes of temperature. 



5 . Breaking by wind, water, etc. 



6. Poisons in soil. 



7. Competitors for favorable position. (The plant is often aided 

 in this struggle by the possession of long roots, ability to grow in 

 shade, etc.) 



Adjustment to Physical Surroundings. 



1. Advantage of greater absorbing surface in vast number of flat- 

 tened organs (foliage leaves), rather than solid compact top. 



2. Similar advantage to plant in having many branched roots in- 

 stead of a single one for absorption and as a hold-fast. 



3. The light relation is especially important, since without sunlight 

 green plants are unable to construct food from the gases of the 

 atmosphere and the substances in plant sap. Methods of growth, 

 therefore, are largely to enable plants to get best position with refer- 

 ence to light to do life-work. 



(a) Plant stems. Two principal methods of development. 



(i) Predominant plants of a region avoid too great shading 

 by elongation of stem = forest as extreme type. 

 Climbing and twining plants. 

 (2) Predominant plants, short-stemmed forms which crowd 

 > each other beneath the soil = prairie as extreme type. 



(Two "societies" — overgrowth and undergrowth — frequently 

 inhabit the same region) . 



(b) Arrangement of leaves . Mat or carpet habits ; leaf mosaics; 

 rosettes ; shape of leaves as modified by relation to one another on 

 tracts; size of leaf with reference to illumination, etc. 



4. Other adjustments must be to heat, the pull of gravity, me- 

 chanical forces (as air and water), moisture, soil, electricity, etc., 

 other phases of which have been included under the heading of self- 

 protection. 



