322 ,REV. GEORGE HENSLOW ON THE 
(s) Self-fertilizing plants are very often annuals, while their allies or intercrossing 
species of the same genus are perennials. In this respect Stellaria media may be compared 
with S. Holostea, Geranium pusillum. Ze, with G. pratense, Polygonum aviculare with 
P. Bistorta and many others. There are, of course, many exceptions, as Malva rotundi- 
Jolia ; but even this species is said to become annual in New Zealand. 1 
(t) ** Weeds” are probably all self-fertilizing or else anemophilous. A weed is simply . - 
an unattractive plant, and possessing no feature worthy of cultivation. 
The following are the chief facts which may be regarded as occurring correlatively 
with self-fertilization, some being actual causes which directly or indirectly bring it 
about :— 
l. The majority of flowering plants can fertilize themselves. 
2. Few plants are known to be physiologically self-sterile with their own pollen. 
3. Many plants bear flowers which are morphologically or structurally self-sterile; the — 
pollen of any such flower, however, is effectual if artificially placed on the stigma of - 
the same flower. 
4. Both physiologically and more or less morphologically self-sterile plants may become 
highly self-fertile under certain conditions, self-fertilization being then correlated with 
or even caused by one or more of the following peculiarities :— 
i. The withering of the corolla after or without any expansion. 
ii. The excision of the corolla with a portion of the stamens (?). 
iii. The partial or even total arrest in development of the corolla, normally present. 
iv. Absence of colour in the corolla. 
v. The corolla closing after expansion. 
vi. The flower-bud never opening. 
vii. In the absence of the proper visiting insects. ` [ climate. 
viii. The reduction of temperature, as in autumn, or by transportation to a cooler 
ix. By grafting on a new stock. 
Highly self-fertile varieties may arise under cultivation or in nature. 
Inconspicuous flowers are highly self-fertile. 
. Cleistogamous flowers are always self-fertilized. 
. Special adaptations occur for securing self-fertilization. 
. Conservation of energy is seen in the reduction of the number of stamens and the 
quantity of pollen in self-fertilizing flowers. 
St The relative fertility may equal or surpass that of crossed plants. d 
l. The fertility does not decrease in successive generations of a plant perpetually 
Been | 
12. The fertility may increase in successive generations, when a more or less self- 
sterile plant has acquired self-fertilizing powers. 
13. Free from competition, self-fertilized plants may be equal to the intercrossed com- 
pared with them either (1) as seedlings, or (2) when planted in the open ground. 
14. Self-fertilized plants sometimes gain no benefit from a cross with the same or 
even a different stock. | 
15. Self-fertilized EN are ə perfectly rcs SG 
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