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 
Fie. 149. Pods of evening 
Fie. 148. Globular clusters of fruits of the primrose 
yCaMONS Ht Tae Maren The open top allows the seeds to 
The cluster at the right is broken, and single escape gradually. Three fourths 
fruits are being carried off by the wind 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 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. 
