168 



INTRODUCTION TO BOTANY 



(Salsola Kali, var. tenuifolia), a most troublesome weed, bears 

 from 20,000 to 200,000 seeds. Taking the moderate estimate 

 of 25,000 seeds to a plant, and supposing all of these seeds 

 to grow into plants equally productive, the offspring of the 

 25,000 individuals would number 625,000,000, and the next 

 generation would number 15,625,000,000,000. Supposing 



FIG. 148. Globular clusters of fruits of the 

 sycamore in late March 



The cluster at the right is hroken, and single 

 fruits are being carried off by the wind 



FIG. 149. Pods of evening 

 primrose 



The open top allows the seeds to 



escape gradually. Three fourths 



natural size 



each plant to have a diameter of about 3 feet and to occupy 

 an area of 7 square feet, the student can readily calculate how 

 many square miles of territory the number of plants last 

 named would cover if actually in contact with one another. 1 



1 To the teacher : If the class will carefully count and estimate the num- 

 ber of seeds produced by some common weeds, and then calculate the 

 number of their possible descendants in the course of five or ten years, 

 the computation will prove most instructive. 



