1897.] NATURAL SCIENCES OF PHILADELPHIA. 185 



lines in diameter. It soon hardens on exposure to the atmosphere, 

 and has a high degree of viscidity from its earliest appearance. 

 Considerable force must be exerted in expelling it from the tissues 

 of the plant. Mr. Darwin's explanation is that in these cases the 

 excretion is for the sake of getting rid of superfluous matter during 

 the chemical changes which go on in the tissues of plants. But as 

 starch is necessary for storage, and plants generally have no super- 

 fluity of the article, why should the plant labor to form that which, 

 in this case, must be the wholly superfluous article of nectar. To 

 get over this difficulty Mr. Darwin had already suggested that nec- 

 tar was in the earlier ages of plant life always superfluous. That 

 insect life at first had no knowledge of its existence or value, and 

 that on discovering it, insects and flowers became gradually more 

 correlated. 



So far as we can now see these secretions render the plant no ser- 

 vice whatever in the great battle of its life, and this Mr. Darwin 

 frankly owns. To him it is an act of excretion of useless matter. 

 To us who believe that individual life is not* wholly for itself, but 

 that every act is of some use in the general economy of nature, the 

 new field opened up is one of extreme interest. Observations in 

 this beautiful field are too limited to warrant any general deduction 

 as to the purpose of these stem-bearing glands. The object of this 

 paper is to draw the attention of those who may have orchidaceous 

 plants to a closer examination of their structure, and to encourage 

 a record of such observations. 



VARYING PHYLLOTAXIS IN THE ELM. 



Calling, a few years ago, the attention, of Dr. John Macfarlane, 

 then assistant botanical instructor in the University of Edin- 

 burgh, to a bed of one year old seedlings of Ulmus Americana and 

 that many of them had opposite leaves, he further observed that 

 each form had been so characterized from the earliest development 

 of the plant. They were either alternate or opposite from infancy, 

 and had adhered strictly each to its separate character through the 

 whole of the first year's growth. This bed of one year seedlings 

 probably contained ten thousand plants. In different parts of this 

 t long bed the numbers of each class varied. In places about one- 

 third were alternate leaved, in others the opposite leaves were much 

 more numerous. For the purposes of this paper it may be assumed 

 that about half were of each class. 



