16 BULLETIN 428, U. S. DEPARTMENT OF AGRICULTURE. 
pods Nos. 7, 8, 9, and 10 in the second row of figure 8. This is a dis- 
tinct type of pod and is found most abundantly in plants having 
medium broad crowns and long and decumbent to ascending stems, 
as shown in figure 18. They are found in S. P. I. Nos. 20726, 26927, 
and 30433. The number of seeds per pod averages approximately 
one more than the average for the species. The seeds are well re- 
tained, and the pods are quite plentifully produced. Plants bearing 
pods of this type set seed more liberally than other forms of the 
species. It must be understood that the two types of pods above 
described represent the extremes and that there are many inter- 
mediate forms. 
Fig. 4.—Seed of Medicago sativa. (Enlarged.) 
Seeds.—In general appearance the seeds closely resemble those of 
Medicago sativa (fig. 4), but a careful examination shows them to be 
appreciably smaller and decidedly more angular. The radicle is also 
more prominent and in some seeds the hilum is very marked, while in 
others it is scarcely apparent. (Fig. 5.) When examined under a 
lens the seeds show a slightly roughened surface. The pitted sur- 
face together with the angular shape produces a feeling of grittiness 
when seeds are rubbed between the thumb and fingers. This is 
especially true of seeds from certain forms of plants. 
The explosive mechanism of the flower is essentially the same as 
that of Medicago sativa, with the exception that more force is re- 
quired to accomplish tripping and usually less energy is expended 
by the column upon becoming released. This condition, together 
