SUPPLEMEN1 



to the distribution of willows, is their habit of striking root so readily 

 that severed twigs are very likely to become new plants. The poplar, 

 or cottonwood, Populus, is nearly related to the willow, as is apparent 

 on examining catkins and fruit. There are several stamens on a 

 disk in each staminate flower, and a pistil may be composed of three 

 or four instead of two carpels. The catkins come early, before the 

 leaves. This tree is not very common in Southern California, but is 

 well worth observation where it does occur. 



The Sycamore, Platanus racemosa^ourn.y alder, Alnus rhombi- 

 folia, Nutt., walnut, Juglans Calif arnica, Wats., or the oak, Quercus, 

 may be studied as typical of wind-pollinated plants. The flowers of 

 the walnut are the easiest to study on account of their size, but it 

 would be unfortunate to miss any of the others that can be observed 

 by the children in the field. The sycamore is one of the most beauti- 

 ful of our canon trees ; it sometimes attains an imposing size ; one is 

 known to be nine feet in diameter. In the spherical flower clusters 

 each pistil or each stamen is a flower. The pollen is protected by the 

 connectives of the anthers, which fit closely together until the pollen 

 is mature and the weather dry ; then, by the shrinking of this tissue, 

 the anthers are sufficiently separated to allow little clouds of pol- 

 len to escape with every breeze. The staminate catkins of the alder 

 mature and fall in December or January, and soon the pistillate 

 clusters become little cone-like fruits ; the leaves come usually in 

 March. The delicate beauty of these straight, slender trees bursting 

 into leaf, is one of the delights of our spring time. Each walnut 

 flower has a calyx, there are many stamens in each staminate flower, 

 and the pistillate flowers have inferior ovaries and minute petals. 



Nearly all wind pollinated plants with staminate catkins have some 

 provision for the temporary deposition of pollen ; the cottonwood 

 has the same device as the walnut ; the anthers of pines and firs 

 deposit pollen on the back of neighboring scales ; the anthers of the 

 sycamore have their connective tissue expanded at the ends like nail 

 heads, and the pollen is lodged here, and so on. The pollen lying in 

 loose little heaps is very easily lifted by the wind, and, as a matter of 

 fact, pollen is best distributed, not by a strong wind, but by gentle 

 rising currents of hot air. About one-tenth of all flowering plants 

 are pollinated by the wind ; some of their characteristics are, small, 

 inconspicuous flower, large stigmas and abundance of pollen, easily 

 accessible to the wind. Bees frequently collect pollen from walnuts 

 and other trees of this class, but they are not likely to be of any 

 service. 



The oak has quite as interesting leaf buds, flowers and fruits as the 



60 



