144 MASSACHUSETTS HORTICULTUEAL SOCIETY. 



Dr. Boweu thought it would be difficult to introduce carbonic 

 acid gas into plant houses without shutting off' ventilation. Owing to 

 the diffusibility of gases, without which we should have layers of 

 gases on the surface of the earth, carbonic acid gas rises from the 

 bottom and mingles with the air. M. Brougniart's theory as to 

 the abundance of carbonic acid gas, and the growth of primeval 

 forests occasioned b}' it, has been very carefully' examined. Tiiis 

 extraordinary luxuriance is one of the greatest curiosities, physio- 

 logically considered, of plant growth. 



Francis H. Appleton said that he had always looked on leaf- 

 mould as most desirable in gardening, but he found it difficult to 

 accumulate enough. 



Dr. Bowen said, in answer to an inquiry, that few animal re- 

 mains are found in coal beds. The gigantic animals appeared 

 later, and were partiallj' dependent on the luxuriant growth of 

 leaves for their support. It is a question whether there were any 

 larger animals in earl^' ages than the whales of the present day. 

 The gigantic lizards were scattered over a long time ; there were 

 cnlj- one or two species at an}- one epoch. 



Henry Xloss said that he had gathered all kinds of leaves, but 

 had thought pine leaves rather injurious to plants. He uses them 

 for covering, but finds them difficult to remove in spring. 



Dr. Bowen knew no reason why pine leaves should be injurious. 

 They would not absorb the sun's rays as much, and they do not 

 contain as much fertilizing material as those of deciduous trees, 

 and lienee tliere might be some difference in two beds covered with 

 these two kinds of leaves. Pine leaves contain a gum whicli is dif- 

 ficult to dissolve, and therefore are longer in decomposing. They 

 make good bculding, though they have not much absorbent proj)- 

 erty. All leaves contain crystals of oxalate of lime, which has a 

 little fertilizing value. 



Mr. Strong remarked that few plants grow under pine trees. 



Dr. Bowen thought this was owing to the thick mulch formed by 

 the pine leaves, and the dense shade, rather than to any injurious 

 substances in the leaves. 



A. W. Cheever said that he had used pine needles as a cover- 

 ing for strawberries, and considered it the best he had ever tried. 

 The}- keep down weeds. He had plouglied them in when he 

 planted corn and other crops with no injurious effect. 



Benjamin G. Smith said that one of the best gardeners in the 

 Society recommended pine leaves as a mulch for strawberries. 



