THE PLANT WORLD 129 



whether this sweet matter is merely a waste product secreted by the gland 

 or whether the power of secreting it has been specially gained by the 

 plant for the sake of attracting ants and wasps which will serve to protect 

 it from caterpillars, leaf-cutting insects, or other enemies.* It seems 

 strange that the glands are of such little structural importance that they 

 may be present in one plant and absent in a closely-allied species, or, as 

 in the case of the Thespesia, that they may be found on some leaves and 

 not on others of the same plant. I was so fortunate while in Central 

 America as to find a gland-bearing Acacia similar to Acacia sphacrocephala 

 described by Belt, if not identical with that species, in the large stipulary 

 thorns of which small ants had taken up their abode. When I broke off 

 a branch I was stung very severely by the tiny insects, which in this 

 case served as a very efficient body-guard. 



In the Kuphorbiaceae of Guam there are at least two plants with 

 glands at the base of the leaf -blade — the common " palma-christi," or 

 castor-oil plant, and the candle-nut tree I saw this afternoon. It seems 

 to me that very little has thus far been done in investigating the subject, 

 and there is a chance for somebody to do some good work. I wish my 

 duties would allow me more time. One thing I have noticed : ants seem 

 plentiful on cotton plants, which also have glandular leaves and sepals ; 

 but I saw none to-day on the Urena, the leaves of which were much 

 eaten by caterpillars. It may be that this species, which has burs with 

 hooked barbs, has been brought to this island by human agency or on the 

 feathers of birds, and that the ants which are its natural protectors have 

 never reached here. It is not surprising that certain insects which lay 

 their eggs in grain, such as the corn and rice weevils, should have gotten 

 here, or that there are plant lice in abundance on some of the introduced 

 foliage plants, which must have been brought here in a growing condi- 

 tion ; but I have thought it very curious and interesting to find on this 

 island a tobacco worm very much like those in America, the larva of a 

 sphinx moth which infests the tobacco plants and keeps the natives busy 

 until the leaves are ready for gathering ; and accompanying the milk- 

 weed, Asclepias curassavica, the same tawny butterfly (^Anosia plexippiis) 

 which feeds on it in tropical America. Both the tobacco and the milk- 

 weed must have gotten here in the form of seed. Eggs of the sphinx 

 moth may have reached here on dry tobacco leaves ; but how did the 

 tawny butterfly get here ? I have also noticed the same insect in Samoa, 

 where the same Asclepias has established itself. 



Friday, September 22. — Action was brought this day by an old woman 

 named Margarita de la Cruz against Bruno del Rosario to recover dam- 

 ages awarded her during the Spanish administration of this island. The 

 wife of Bruno, it seems, assaulted the old lady and set her house on fire. 



Darwin, "Cross and Self Fertilisation in the Vegetable Kingdom," p. 402-4. New York, 1877. 



