* \ y \ be... » } ~<a 1 on a ye To a ne, 
\ Nl ‘ nN ‘ o wo Fi 
S ‘ . < , ps % é 
. : ; : ae, a : : pes So. eae 
S i ye ’ 
; 
186 Structural and Physiological Botany. 
frequently actually found in nature. The main support of this view is 
found in the phenomena of dichogamy and heterostylism, which are 
found to occur in so many plants. 
By dichogamy is meant the maturing at different times of the re- 
productive organs in a hermaphrodite flower. Dichogamous flowers 
are either protandrous, when the pollen escapes from the anthers before 
the stigma in the same flower is ready for fertilisation, or Arotogynous, 
when the stigma has lost its capacity for fertilisation before the pollen 
is mature, so that its fertilisation must depend on the pollen of older 
flowers. Most species of Geranium, Pelargonium, Malva, Umbelliferee, 
Composite, and Campanulacex, are protandrous ; while among proto- 
gynous plants [which are much less common] may be mentioned 
species of Magnolia, Aristolochia [Scrophularia, Plantago|, &c. 
fleterostylism consists in different flowers belonging to the same 
species having stamens and pistils (styles) of different lengths. Thus, 
for example, in the cowslip [and primrose], zum perenne, and 
Pulmonaria officinalis (Fig. 357), two different forms occur, the long- 
Fic. 357.—Dimorphic flower of Pzdmonaria: 1. long-styled ; II. short- styled form; 
a corolla; J anthers ; ¢ ring of hairs; @ pistil. 
styled (1.), and the short-styled (11.). This difference in the form of the 
reproductive organs is called dimorphism ; while trimorphism, or the 
existence of three different forms, occurs in Lythrum Salicaria [and 
Oxalis|. In plants in which this arrangement occurs, fertilisation, 
or the production of fertile seeds, is, as a rule, effected only by the 
union of the reproductive organs which stand at the same height, and 
which are therefore always found in different flowers (Fig. 357 1. 6 and 
11. @, and I. d and Il. 4) ; [it is obvious that this will easily be brought 
about by theagency of insects.] Finally the circumstance is specially note- 
