PHYSIOLOGICAL PROCESSES IN PLANTS 45 

 2. SPECIAL DIRECTIONS FOR THE STUDY OF SOME FALL 



FLOWERS. 1 



Field Flowers. Let us now take up some common wild flowers easily 

 found in the fall of the year, and work out the relation of the parts of the 

 flower to its insect visitors. Remember that the important part of these 

 exercises is to find how and by what means the flower is adapted or fitted 

 to receive the visits of insects. This work can be done best on field trips, 

 but it can readily be modified so as to be useful as a schoolroom ex- 

 ercise. 



The Evening Primrose ( Onagra biennis~) . The habitat preferred by 

 this flower is dry fields, roadsides, or waste places. The yellow flowers 

 are found in long, upright, densely crowded clusters. A flower cluster 

 in which the individual flowers have no flower stalks or pedicles, with 

 one main axis to the cluster, is called a spike. Notice that young and 

 old flowers and fruits are all on the same cluster. Where are the 

 youngest flowers located in the cluster? Is there any flower at the 

 end of the main stalk ? Could you determine in advance the length of 

 the flower cluster ? Such a cluster is said to be indeterminate. Why ? 

 Study a single open flower. Note the calyx and corolla ; are the parts 

 distinct ? How many petals do you find ? Notice that there are eight 

 stamens and that the stigma is four-parted. Cut the ovary in cross 

 section, and see how many locules (spaces) there are. 



When a flower has each circle of parts, as the sepals, petals, stamens, 

 and pistils, made up of a certain number of divisions, or when they 

 appear in multiples of that number, the flower is said to be symmetrical. 

 Here we see a very striking example of symmetry in a flower. 



The chief attraction to insects is the nectar, which is formed in nectar 

 glands at tl.e base inside the slender tubular corolla. Information is 

 given to the insects of the contents by a faint, sweet odor. This flower 

 is not visited by many day-flying insects. Can you determine the 

 names of any that do come by day? At night the flower opens more 

 widely and the scent becomes much more noticeable. Moths are its 

 chief night visitors. The long proboscis is thrust into the flower and 

 quickly withdrawn, but usually a little pollen is carried off on the palps 

 (projections on the sides of the head). This maybe left on the next 

 flower visited. 



Try to determine what other insects, if any, visit the evening primrose 

 at night. 



Draw a single flower split open lengthwise to show the position of the 

 parts, and especially any adaptations to insect pollination. Look for 

 any special means for the prevention of self-pollination. Label all the 

 parts. 



Moth Mullein (Verbascum Uatiaria}. The moth mullein is one of 

 the most beautiful weeds, despite the fact that few blossoms are found at 

 any given time. The plant flourishes on dry, waste land, roadsides, and 

 open fields. It was introduced into this country and has since become 

 common here and in Canada. 



The flowers are found in a long, loose raceme. A raceme is like a 

 spike, except that each flower has its own flower stalk developed. Has 



1 Adapted from Hunter, Elements of Biology. 



