A pine cone tale

April 7, 2010

A major goal of Montessori botany studies is to help children learn to observe and understand plant structures. There are a lot of things going on in the plant world that take a sharp eye and careful observation to find. The life cycle of pines is one of them. It is important for the teacher/guide to show children inconspicuous plant structures such as pine cones throughout the year and explain to them what is happening.

Most people are familiar with conifer cones, although they tend to call all of them “pine cones.” Few have followed the development of a cone through the year – or two years in the case of pines – that it takes for a cone to mature. I have been photographing the development of pine cones and here’s a look at their life cycle.

Pines have two kinds of cones on the same tree, pollen cones and seed cones. The latter are formally called ovulate cones. The trees don’t usually form cones every year. In cone years, the cycle begins as the new shoots elongate in the spring. The seed cones form at the end of the new growth. They look like tiny pink-to-purple bristles.

These are young seed (ovulate) cones on the new shoot of a ponderosa pine.

The pollen cones cluster at the base of the new shoots, beneath the terminal bud. Most of the pollen cones form on the lower branches of the tree, away from the seed cones, but sometimes they form on the same shoot as the seed cones. The wind usually won’t take pollen from the base of the tree to its upper branches, so the arrangement of seed and pollen cones encourages cross-pollination. 

These two cones formed in the previous spring. The one on the right died during the winter. The left one is starting to grow.

  

By early July, the living seed cone has quadrupled in size. Its scales are noticeably green.

Conifers use wind pollination, which requires a lot of pollen to work, and in cone years the trees produce an amazing amount of pollen. Pollen cones tremendously outnumber seed cones. After they release their pollen, most of the spent pollen cones drop off the tree. You can sometimes find dried ones in the branches later in the summer, however.

It takes careful observation to find the budding ovulate cones, even though they can be colorful. They hide among the new needles and are most easily seen from above, the bird’s eye view we don’t usually have. It doesn’t help that the ovulate cones usually form on the higher branches. You may need to pull a branch down so that the children can see the tiny new cones. The little cones of pines don’t grow much during their first year. In the fall, they have become browner and drier looking, but are nearly the same size as they were in the spring.

In the second spring the pine seed cones rapidly enlarge. A shoot I photographed had a pair of seed cones, but one of them had died. It provides a size scale to show how much the live cone has grown. Fertilization is a slow process in pines. It takes about 15 months for the egg cells to form and the pollen tube to grow and deliver the sperm to the eggs. The scales of the seed cones are green until late fall. By that time the seeds are mature. The cone dries and the scales spread apart, releasing the winged seeds. The dried cone may remain on the tree for months or years, until a strong wind brings it down.

In the fall, the seed cone has dried. Its brown scales spread apart and the seeds are released.

In case you need help finding your local pines, look for a conifer tree with needles in bundles of two to five. Other conifers, such as firs or spruces bear their needles singly. Their cones mature in one year, but they can be even harder to see because the seed cones form in the tops of the tree.

Take a look around this spring and see if you can locate some young cones to show your children and to follow through the cone life cycle.

The winged seeds of the pines blend in with the soil and rocks very well.


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