Occurrence and specialization of vessels in Xyridales

The occurrence and variation among vessels in available parts of 41 species in 16 genera of Rapateaceae and of 20 species in the four genera of Xyridaceae were determined. The vessels in Xyridaceae are more specialized in all organs of the plant than they are in Rapateaceae. Simple and scalariform perforation plates occur in the inflorescence axes and leaves of nearly all species of Xyridaceae but only scalariform plates occur in these organs of Rapateaceae – infrequently vessels are lacking in stems and leaves, at least in early metaxylem. Vessels in roots and stems of Mono–tremeae are most specialized (simple and scalariform plates) among tribes of Rapateaceae, with those in Rapateeae intermediate, and those in Schoenocephalieae and Saxofridericieae most primitive (only scalariform perforation plates). Brief comments are made about vessels as possible indicators of relationships with other families.     

The mechanics of hopping by kangaroos (Macropodidae)

Force platform records and films have been made of kangaroos and a wallaby hopping.
The maximum forces exerted on the ground were about six times body weight. The force exerted on the ground changes direction, throughout the period when the feet are on the ground, so that it is always more or less in line with the centre of mass. Consequently the animal decelerates a little and then accelerates again, during the contact phase.
The fluctuations of potential energy which occur in each hop are slightly smaller at high speeds than at low ones. Fluctuations of external kinetic energy increase with speed and account for most of the energy cost of hopping at high speeds. Fluctuations of internal kinetic energy (due to acceleration and deceleration of the limbs) are relatively small. While the feet are on the ground the extensor muscles of the hip do positive work, those of the knee negative work and those of the ankle negative work followed by positive work. The energy cost of hopping is reduced substantially by elastic storage of energy in the Achilles tendon. In the case of a wallaby hopping at moderate speed the calculated saving was 40%. The maximum stresses developed in leg muscles, tendons and the tibia have been calculated and are discussed in relation to the known properties of muscle, tendon and bone. The trunk pitches as the animal hops because the two legs swing forwards and back simultaneously. Appropriate tail movements reduce, but do not eliminate, this effect. A mathematical theory of hopping is presented and used to investigate the merits of different hopping techniques.
Dawson & Taylor's (1973) discovery that the rate of oxygen consumption of kangaroos decreases a little, as hopping speed increases, is probably to be explained by the increased role of elastic storage of energy at high speeds.