1893.] the origin of this and similar phenomena. 131 



in West Flanders. Darwin^ found it frequent in Kent, while 

 in Cambridgeshire during the last few years, the author has found 

 it very much more common than the hermaphrodite form. 



Prunella vulgaris L. — The author has never observed a female 

 plant in England, though great numbers have been examined. 

 On the Continent it seems to be frequently female. 



If we sum up the results of these and other observations upon 

 gynodio3cism and gynomonoecism, we may come to the following 

 conclusions. They are very wide spread phenomena, but in a 

 large number of cases where they occur, seem only to be sporadic. 

 In a few cases, e.g. many of the Labiatse, and possibly other 

 orders, the phenomena are pretty regularly shown, and appear 

 to be fixed by heredity. In all cases, however, they are very 

 variable ; this is well seen in the observations given above, and 

 in those of Schulz", Ludwig, Loew and other writers. Causes 

 of variation appear to be soil, temperature, light, climate and 

 causes internal to the plant itself, all acting upon and deter- 

 mining the immediate cause, which may be differences in nu- 

 trition of the flower primordia. 



The female flowers in the Labiatse are as much visited as 

 the hermaphrodite, and set many seeds ; according to Darwin 

 more than the hermaphrodite, according to Schulz not so. In 

 these cases it is therefore probable that it is a distinct advantage 

 to the plant to possess the two forms. In other cases the ad- 

 vantage seems rather doubtful. It is noteworthy that a large 

 proportion of gynodioecious plants are perennials with good vege- 

 tative reproduction. 



With regard to the origin of these phenomena, there has been 

 much discussion. Muller's view has now been entirely abandoned 

 and need not be considered. Hildebrand and Ludwig regard 

 it as an outcome of dichogamy : most of the plants exhibiting 

 it are protandrous and the stamens of the first flowers are there- 

 fore useless and may become aborted. This view Ludwig supports 

 by his observation that in Thymus the female plants bear a larger 

 proportion to the hermaphrodites at the beginning of the season 

 than later on. The author made some observations upon Nepeta 

 Glechoma (see 1st paper) which tended to confirm this view. 

 These have been continued and now afford the following Table 

 [the numbers represent percentage (of the total number of plants 

 in flower) of female plants in flower]. 

 Week 12 3 4 



1891 50- 16- 35-8 28*5 



1892 57- 30-9 25-8 292 



1893 37-5 25- 168 143 68 313 31- 20 



1 " Forms of Flowers," p. 305. 



- "Beitrage zur Kenntniss d. Bestaubungseinrichtuiigen u. d. Geschlechterver- 

 theilungen bei den Pflanzen." Bihliotheca Botanica, Heft 11 u. 17. 



10—2 



