186 THE PIvANT WORLD 



forms are apparently insignificant, and so do not call attention to them- 

 selves except from those who have given them some study. A little 

 experience, however, in collecting them, and a fair amount of inquiry 

 into their structure and habits, will put one into possession of an inter- 

 esting and, for teaching, very useful body of knowledge. 



One of the least widely known phases of the biology of the Liverworts 

 is their ability to withstand drought, and the correlated structural modi- 

 fications, which in some cases are to be found, are well worthy of note. 

 We are glad, therefore, to direct attention to an article upon this subject 

 by the well known student of these and allied organisms. Professor D. 

 H. Campbell, to be found in the recent issue of Torreya.* Attention is 

 directed in this paper more especially to the behavior of the hepatics of 

 California. The species found in the region of San Francisco Bay are 

 able to withstand, with little or no harm, the protracted drought of the 

 summer season, which sometimes extends over a period of six months. 

 Although the heat is not excessive, and the dryness is mitigated by the 

 mists from the ocean, the conditions are such that the hepatics remain 

 quite dried up and dormant. When the rains commence they regain 

 their turgid condition, and in a few hours growth recommences, as 

 appears from a careful study of two species by Mr. H. B. Humphrey. 

 The sexual organs, which are sometimes present during the dry season, 

 develop and mature in about two weeks. These plants were also shown 

 by experimental methods to be able to resist decimation much greater 

 than to which they are normally exposed. 



Special devices are to be found in some forms for protection against 

 the excessive loss of water. Among such may be classed the hairs or 

 scales which protect the growing point. These sometimes secrete a 

 mucilage, as do also certain cells within the tissue of the plant, and this 

 secretion has probably a role to play in the storage of water. Anthoceros, 

 for example, secretes a large amount of mucilage, and this is very probably 

 important in this way, and the colonies of the gelatinous alga Nostoc, 

 which are to be found in the Anthoceros , may also be interpreted as 

 analogous to the mucilage cells proper of this plant. Geothallus , a plant 

 which is adapted to the still dryer climate of southern California, has the 

 ability to form a peculiar tuberous structure. This is formed by the 

 enlargement of the interior tissues, which become loaded with reserve 

 food, and these are protected by a rind developed from the outer cells. 

 The thallus, with the exception of a small growing point near the tuler, 

 dies away, and from this growing point a new plant is developed upon 

 the return of the necessary moisture condition. Members of certain 

 other genera behave similarly. 



It is very instructive also that the prothallia of certain ferns are able 



• 4 : 8i-86, June, 1904. 



