The Rhythmic Nature of Animals 
and Plants! 
By Frank A. Brown, Jr. 
Morrison Professor of the Biological Sciences 
Northwestern University 
The Year's Awakening* 
“How do you know that the pilgrim track 
Along the belting zodiac 
Swept by the sun in his seeming rounds 
Is traced by now to the Fishes’ bounds 
And into the Ram, when weeks of cloud 
Have wrapt the sky ina clammy shroud, 
And never as yet a tinct of spring 
Has shown in the Earth’s apparelling ; 
O vespering bird, how do you know, 
How do you know? 
How do you know, deep underground, 
Hid in your bed from sight and sound, 
Without a turn in temperature, 
With weather life can scare endure, 
That light has won a fraction’s strength, 
And day put on some moment’s length, 
Whereof in merest rote will come, 
Weeks hence, mild airs that do not numb, 
O crocus root, how do you know, 
How do you know ?” 
THOMAS HARDY 
Lavine Toinés inhabit a world replete with rhythms. Nearly every 
aspect of the physical environment exhibits rhythmic changes. From 
the submicroscopie atoms, comprising systems of negatively charged 
1 Research program on rhythmicity was aided by a contract between the Office of Naval 
Research, Department of the Navy, and Northwestern University. This article reprinted 
by permission from Northwestern University Tri-Quarterly, vol. 1, No. 1, fall 1958. 
*From Satires of Circumstance, copyright, 1914, 1925, by the Macmillan Co. Reprinted 
by permission of the publishers. 
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