318 Floristik, etc. — Angewandte Botanik. 



Verf. gibt eine ausführliche Liste der Pflanzenreste des Tonfe 

 (69 Nummern) und stellt die Pflanzengesellschaften von fünf Hori- 

 zonten zusammen, woraus er dann Schlüsse auf Klima, Wasser und 

 Landschaft der Rabutzer Gegend zieht, 



W. Herter (Berlin-Steglitz). 



Harrington, G. T., Agricultural value of impermeable 

 seeds. (Journ. agr. Research. Washington. VI. p. 761—796. 1916.) 



The Contents of this paper is summarized by the writer in the 

 foUowing conclusion: 



By "impermeable seeds" is meant those seeds all parts of whose 

 seed coats are impermeable to water at temperatures favorable for 

 germination. It is impossible to distinguish between impermeable 

 and permeable seeds except by testing their ability to absorb water 

 at a temperature favorable for germination, The production of 

 impermeable seeds is particularly characteristic of the Leguminosae , 

 but it occurs also in many other plant families. Among the cultivated 

 species which sometimes produce impermeable seeds are okra {Hibis- 

 CHS esculentus L.), hollyhock {Althea /'ose« (L.)Cav.), alfilaria (E'ro^/wm 

 cicutarium (L.) L'H^r,), atriplex {Atriplex spp.), asparagus {Asparagns 

 officinalis L.), morning-glory {Iponiea purptirea (L.) Lam.), canna 

 [Canna indica L.), cherrytomato {Physnlis piibescens L.) and nearly 

 all of the cultivated species of Leguminosae. 



Impermeable seeds frequently retain their vitality for many 

 years, sometimes for at least as many as 80 years. Fresh imper- 

 meable seeds germinate promptly when the seed coat is broken or 

 becomes permeable. The viability of fresh impermeable seeds is 

 frequently greater than the viability of fresh seeds of the same 

 species which are permeable. 



Seeds of the common clovers, alfalfa {Medicago sativa L.), and 

 hairy vetch {Vicia villosa Roth.) which are impermeable at the end 

 of three to five years under laboratory conditions of storage retain 

 their vitality apparently unimpaired up to that time. The viability 

 of the permeable seeds in the same lots decreases slightly in the 

 second and third year and more in subsequent years. In dry storage 

 nearly all impermeable alsike-clover {Trifolium hybridum L.), white 

 clover (7>. repens L.) and sweet clover {Melilotus alba Desv.) seeds 

 remain impermeable until at least 2 or 3 years old. Impermeable 

 red-clover seeds {Tr. pratense L.) become permeable gradually in 

 dry storage, but from one third to two-thirds of them may still 

 be impermeable after four j^ears. The majority of impermeable 

 alfalfa and hairy-vetch seeds become permeable before they are 

 2 years old, Okra seeds become less permeable as their age increases. 



In wet blotters nearly all impermeable alfalfa, crimsonclover, 

 hairy-vetch and okra seeds soften and germinate in one year, 

 though a very few may remain impermeable even after three or 

 four years. Impermeable seeds of red clover, alsike clover, white 

 clover and sweet clover soften and germinate more slowly, but 

 with no uniformity as to rate. All germinate within one year in 

 some cases, while in other cases over 50 per cent are still imper- 

 meable after four years. 



Impermeable clover seeds which were thoroughly matured 

 before harvesting soften and germinate more slowly under conditions 

 favorable for germination than do impermeable seeds of the same 

 species which were less well matured; they also become permeable 



