Tricks that help plants reproduce
The ''clever'' strategies by which plants propagate inspire continuing amazement. But who expected pine trees to be skilled aerodynamicists or seeds of many other plants to ''use'' ants, beetles, worms, and snails to survive?
At least some pines, it seems, have evolved intricate designs of pollen grains and cones that help a species to capture its own wind-borne pollen. Karl J. Niklas of Cornell University and Kyaw Tha Paw U of Purdue University have found that the aerodynamic characteristics of pollen grains, such as settling speed and the air flow around ovule-bearing cone scales, favor such pollen capture. A species' own pollen is preferentially caught by the eddies and swirls of air flowing past the cones.
In describing their studies in the journal Science, they note that other factors, such as adhesion or surface roughness, also help. Nevertheless, with the help of wind-tunnel studies, they found what they consider strong support for the view that pollen grains and cone structure are aerodynamically matched. ''. . . Wind pollination in the conifers appears to be a quite sophisticated and aerodynamically interactive system,'' they say.
Equally intriguing is the extent to which ants and some other invertebrates help seeds to survive. It has long been known that birds, bats, and some other animals distribute seeds widely. Many an oak has sprung from a squirrel-buried acorn. What has not been fully appreciated is the extent to which many plant seeds rely on the protection of ant nests and the nourishment they provide, or on being buried by beetles and embedded in the castings of earthworms and snails.
Andrew J. Beattie and David C. Culver of Northwestern University call this survival strategy ''inhumation'' - a term which also covers passage of seeds through the gut of birds, bats, and other mammals. Reporting on their research in Nature this past summer, they suggest that ''the inclusion of major and abundant invertebrate groups . . . may make the process of inhumation far more important than previously supposed.''
Seeds that make themselves attractive to ants tend to have nutritious outer coverings. Ants take such seeds home, eat this covering, and abandon the still viable seed in an old gallery or refuse pile. This removes the seed from the surface, where some animal might eat it, and places it in a nutritious and protected environment. Messrs. Beattie and Culver find that such seeds are more likely to produce vigorous seedlings than those that sprout from the surface.
Thus inhumation not only enhances seed survival, but helps ensure that seeds will be planted in environments that are relatively rich in such critical plant nutrients as phosphorus, potassium, and nitrogen, the two scientists say.
Here is a seed survival strategy that, while previously known, may be far more important than has been suspected. Along with the sophisticated aerodynamics of pine cones, it shows that plants still have many secrets to be discovered and amaze us.