38 



SCIENCE-GOSSIP. 



CONTRIBUTIONS TO THE LIFE-HISTORIES OF PLANTS. 



By Thomas Meehan. 

 (Continued from page 16J 



Fecundity of Heliophytum. 



TTELIOPHYTUM INDICUM, the Heliotropium 

 indicum of the older botanists, has found its 

 way over all the tropical and subtropical portions 

 of the earth. It is at home in Asia, Africa and 

 America, and if it once gets a chance seed into the 

 soil of Europe, will no doubt as easily maintain its 

 hold as other free-seeding typical weeds have done. 

 In some unknown way a few plants appeared in 

 1S94 in my garden (Philadelphia), and have afforded 

 me an interesting study. Its capacity for seed 

 production is enormous. The cyme-branches that 

 have flowered and have, or will have, perfect seed, 

 represent, August 2Sth, a line of 1,224 inches. 

 There are twenty seed vessels, that is to say forty 

 seeds to the inch, making a total of 46,960 seeds. 

 The cymes are still vigorously unfolding and 

 flowering, and will probably double these figures, 

 but in uncertainties it is best to be on the safe 

 side ; so, allowing but one-third more, we have a 

 length of fruiting rachis of 1,632 inches, and a 

 total seed production of 65,280. 



All this has proceeded from a plant that was 

 itself but a seed three months before! The total 

 length of stem and branches supporting these 

 seed-bearing cymes is but 396 inches. The plant 

 is true to the classical story of Clytie and Phoebus 

 which gave the original genus Heliotropium its 

 name. It does not open a flower until the sun has 

 reached the summer solstice. When the sun 

 ceases to woo it, the flower opens, only to find its 

 beloved going away. Less than three months of 

 flowering will, therefore, have been occupied in 

 this enormous seed production. 



The facts here detailed have an important 

 bearing on two points maintained by me in 

 connection with the life-history of plants. 



I have recorded numerous observations in the 

 "Proceedings" of the Philadelphia Academy, 

 commencing with 1S66, showing that the growth- 

 energy of plants is rhythmic, dependent on the 

 power of the plant, or the parts thereof, to 

 convert nutrition into the growth-force, and 

 that the various forms which plants present 

 are the result of varying phases of life-energy, 

 in most cases of no physiological value, and 

 with which environment has little to do. The 

 evidence furnished by Heliophytum, though of 

 a negative character, is surely strong! Through 

 the long ages the plant has been established 

 over a vast area, and consequently subjected 



to many varying and varied conditions of environ- 

 ment, it has continued as a compact genus or 

 section distinct from Heliotropium, without any 

 material change that would warrant a modern 

 botanist in making a new species of it. 



Again, it has been maintained by me that as 

 environment can have no important influence on 

 changes of form, the free and untrammelled pro- 

 duction of seed would be of far more importance 

 in a supposed " struggle for life" than any power 

 of adaptation could be that depended more on an 

 occasional cross for its increased energy. Dean 

 Swift's satire, in which the Lilliputians by the 

 mere force of numbers are made to overcome the 

 giant Brobdingnagians, cannot be supported in 

 every case by the histories of plants ; but when it 

 comes to a question of distribution, numbers 

 surely are the more likely to hold the field. 



I think I may claim the credit of advancing the 

 further proposition that a free production of seed 

 may always be taken as an a priori indication of 

 self-fertilization. In cleistogamic flowers the 

 certainty of seed-bearing is well known. With 

 rare exceptions the huge natural order of Com- 

 positae are self-fertilizers, and they have managed 

 to embrace within themselves about one-tenth of 

 the whole vegetable kingdom. Where the wind or 

 an insect is the agent in fertilization, the agent 

 does not always come along. On plants depen- 

 dent on this outside assistance, numerous flowers 

 fail to seed. No plant so dependent ever perfects 

 all its seeds; in many cases utter failure follows. 

 In this remarkable plant there is no indication that 

 a single flower failed to mature seed. It must 

 certainly be held remarkable that in a single plant, 

 bearing in round numbers over 30,000 flowers, 

 every one should bear two seeds. 



It has been contended that, though plants may 

 generally self-fertilize when the agents for cross- 

 fertilization do not attend, they are so arranged as 

 to cross-fertilize when the agent does appear. As 

 the Heliophytum flowers are freely visited at times 

 on my grounds by insects, and especially butterflies, 

 there might be some strength in the point. I can, 

 however, testify by an almost daily observation of 

 my plant through the season, that minute flowers 

 are only visited by insects when others are scarce. 

 Though I have seen them visiting the flowers for 

 several successive days, there are many days when 

 they do not visit them, and none were noticed on 

 the former until the beginning of August. A careful 

 watching of the anthers shows, however, the extreme 



