32 THE AMERICAN BOTANIST 



club mosses and scouring rushes. The Pteropsida, on the con- 

 trary, produced large leaves with sporangia on the backs of 

 the sporophylls. This group originated seeds and is regarded 

 as the parent stock from which came the flowering plants and 

 ferns. As far back as we have been able to penetrate the geo- 

 logical record, the two groups of plants mentioned appear to 

 have existed, side by side, but in all cases to have been quite 

 distinct from each other. It is popularly supposed that a great 

 share of the plants which formed the coal were ferns, but this 

 is probably a mistake. Most of the fern-like plants of the coal 

 age were really seed-plants with leaves resembling the ferns. 



Evolution of the Larch. — Most of our coniferous 

 trees, or Gymnosperms, retain their leaves during the winter. 

 So well known is this habit that the members of the group are 

 often called evergreens in common parlance. There are, how- 

 ever, a number of trees that prove conspicuous exceptions to 

 this rule, among which are the American larch (Larix larkina), 

 the European larch {Larix Europaca), and the cypress (Tax- 

 odiuui (listichum). These cast off their leaves at the end of 

 the growing season. Whether they have always been decidu- 

 ous, or whether they have gradually adopted the deciduous 

 habit is therefore, an interesting question. Some light is 

 thrown upon the subject, however, by the behaviour of young 

 larch seedlings. It is well known that plants in the immature 

 condition often run through more or less rapidly former con- 

 ditions of existence. Thus the young cactus plant may pro- 

 duce true leaves and only later take on the usual cactus form. 

 Larch seedlings appear to be no exception to this rule. For 

 some years after the seeds have sprouted, the plants retain 

 their leaves through the winter, but when older, they throw 

 them off. It seems, therefore, that the larches were once like 

 the other evergreen cone-bearers, and have since adopted the 

 deciduous habit. A similar condition exists today among 

 genera represented in both the tropics and temperate zones. 



