OCTOBKR 12, 1!^S3.] 



SCIENCE. 



493 



and lit'ty-eight, tluee-lol)ed ; and scvcutv-ninc. 

 • mitten form.' 



The first leaves of spring were iiivarialily 

 entire, and a lolied leaf was rarely found until 

 the fourth leaf was passed in counting from the 

 base of the branch toward the tip. No regular 

 order was discovered. In one case the arrange- 

 ment was as follows : three entire, four three- 

 lobed. one 'mitten.' one three-lobed, one 

 ' mitten,' one tlirec-lobed, one ' mitten,' one 

 three-lobed ; on another branch, four entire, 

 one • mitten,' five three-lobed, one ' mitten,' 

 three three-lobed, three • mittens.' The 

 leaves on short spurs of old trees were nearly 

 all small and entire ; when the branches were 

 somewhat longer, and the leaves larger, there 

 were one or more three-lobed or ' mitten ' 

 leaves in the middle of the stem. A number 

 of branches taken from slow-growing trees 

 gave the following aggregate : entire leaves, 

 seventy: 'mittens,' sLs ; three-lobed leaves, 

 three. A vigorous young sprout gave twenty- 

 seven three-lobed leaves, one ' mitten ' near 

 the middle of the stem, and no entire leaves. 

 Another had two entire blades at the base, and 

 twelve three-lobed leaves above. A number 

 of these rapidly-growing young trees together 

 gave twenty-seven entire leaves, fourteen • mit- 

 tens,' and eighty-one three-lobed leaves. 



The entire and smaller leaves are in the 

 majority on slowly-growing trees ; while, on the 

 young sjjrouts, larger three-lobed leaves pre- 

 dominate. The • mitten ' form is mostly found 

 with the entire leaves. This form of leaf is 

 probalily about equally divided between the 

 ■ right-handed ' and • left-handed ; ' though, of 

 the number found (seventy-nine), those with 

 the 'thumb ' to the left, when held with under 

 side upward, exceeded the other sort by half. 

 About every thirteenth leaf is a ' mitten.' — a 

 form not found mentioned in the botanical de- 

 scription of the sassafras. 



There seems to be no order in the arrange- 

 ment of the three forms upon the branch. 

 Leaves from the buds were examined, and all 

 of tlie three forms were found. Each kind is 

 distinct, from a very early state ; and there is 

 no indication that one ever passes into the oth- 

 er. No intermediate forms have been found. 

 The venation of the three forms is very much 

 the same. There is a midrib running length- 

 wise through the leaf, and a strong lateral vein 

 on each side, which nms from near the base 

 to beyond the middle of the leaf. Smaller 

 veins form the framework of the middle and 

 upper parts of the leaf. The portion of par- 

 enchyma absent in a lobcd leaf is midway 

 between the strong lateral veins. This is 



very clearly shown in a ' mitten,' where one 

 side is lobed, and the other entire. It would 

 seem as if the lobing is a failure to fill up 

 the framework, and apparently due to a too 

 vigorous growth of the veins, and a lack of 

 a sullicieni amount of the soft, tilling tissue. 

 In the formation of leaves the sassafras is 

 certainly ' at loose ends,' but in this it is not 

 alone. 



Fig. 1 shows an entire sassafras-leaf; fig. 

 2, a three-lobed leaf; and fig. 3, a 'mitten.' 

 Fig. 4 shows the young leaves of the three 

 forms. All the illustrations are drawn from 

 natiu'e. Uvron D. Hai.stkd. 



Nfw York, July -J. 18S:J. 



THE UNITS OF MASS AND FORCE. 



In the original definition of the gram it was 

 regarded as a weight, and therefore a force, 

 being the weight at the level of the sea, and 

 at the latitude of 45°, of .one cubic centimetre 

 of water at its maximum densit}'. It was thus 

 virtuallj' defined as a force. But as we shall 

 soon see, although defined as a unit of force, 

 it has become in practice a unit of mass. In 

 the C. G. S. system of units this change is 

 accepted, and the definition is modified accord- 

 ingl^v ; that is, one cubic centimetre of water 

 is taken as the unit of mass, and this mass is 

 called the gram without reference to its weight. 



In volume i., C'oiirs <Je physique, M. Jamin 

 criticises this change. The high standing and 

 character of this great work, as well as the emi- 

 nence of its author, entitle his views to respect- 

 ful consideration, especially as the question 

 involves the fundamental elementary concep- 

 tions of physics in a way to render it of inter- 

 est to the general student. 



AVe set out with the proposition that what 

 we commonly consider units of weight, such as 

 the kilogram and pound, practically become 

 units of mass in all the ordinary affairs of life. 

 The reason is, that in practice bodies are 

 weighed by balancing them against pieces of 

 metal, and not by means of a spring balance, 

 A pound weight is indeed heavier the farther 

 north we go ; but then, whatever we weigh 

 with it is heavier in the same ratio. Accord- 

 ingly, if by means of a weight we weigh a 

 pound of tea at the equator, iit. the poles it 

 will still weigh the same as a pound weight, 

 although in reality heavier than at the equator. 

 This is obviously a great practical and com- 

 mercial convenience ; because the quantity or 

 mass of the tea is the important question to 

 those who deal in it. while its gravitating force 

 is of secondary importance. Were a perfect 



