CYC AD ALES 79 



duration of the crown is known. Unfortunately, this period is seldom 

 known. People in cycad localities know that new crowns appear 

 every year, but have not noticed how often any individual plant 

 forms a crown. Records of conservatory plants are worthless because 

 leaves last much longer than in the field. The duration of the crown 

 and the average number of leaves in a crown, under natural condi- 

 tions, furnish a basis for an approximate estimate of the age. 



In Dioon edule a new crown is formed every other year, and the 

 average number of leaves in the crown of an adult plant is about 20, 

 so that the average is 10 leaves a year. If the number of leaf bases is 

 10,000, the plant is about 1,000 years old. The number of leaves 

 produced while the plant is young is much smaller and as it reaches 

 the coning age it may produce a cone and a crown of leaves at the 

 same time, thus reducing its vitality so that it may go into a dormant 

 condition, producing neither cones nor leaves for several years. It 

 is evident that estimates made in this way are likely to be conserva- 

 tive. 



Plants of Dioon edule less than 2 meters in height, like the speci- 

 men shown in fig. ^4, may be 1,000 years old. Plants in protected 

 ravines may be much older. Dioon spinulosum, more than 10 meters 

 in height, may not be more than 200 years old. 



Three plants of Encephalartos altensteinii and two of E. latifrons, 

 in front of a residence at Trapps Valley, South Africa, under prac- 

 tically field conditions, had been under observation for 46 years in 

 191 2. The owner said that the E. altensteinii might have grown 6 

 inches, but that the E. latifrons did not seem to have grown at all, 

 although all of the plants had had green leaves all the time and had 

 occasionally produced cones. 



There seems to be no way of estimating the age of those tuberous 

 forms which have no persistent armor of leaf bases. Naturally, the 

 tuberous forms are comparatively small, but it is possible that they 

 may reach a great age. The stem of Bowenia serrulata is more or less 

 spherical, and is often 20 cm. in diameter, with occasional specimens 

 twice that size. Bowenia spectahilis does not reach so great a diam- 

 eter, but is often 30 cm. in length (figs. 68, 69). Stangeria and the 

 tuberous species of Zamia have the same general shape of stem as 

 Bowenia spectahilis. 



