326 Nutrition and Selection. 



flowerheads of composites, and so forth. Every shoot 

 has its cycle. It begins with simple or atavistic forms, 

 then gradually manifests the characters which are pecu- 

 liar to the species in their full development, and gradually 

 reverts. From the primary shoot this cycle is transmitted 

 to the secondary shoots and from these to the branches 

 of still higher orders. In this process the latter may 

 become stronger or weaker in comparison with the main 

 shoot, or even of equal strength. As a rule the branches 

 are weaker than the main shoot ; those which are not fall 

 into two categories according to Braun^ strengthened 

 shoots and repeating shoots {Erstarkungssprosse and 

 Wiedcrlwlungssprossc).^ Spikes and racemes are the 

 best known instances of weakened shoots ; their apical 

 flowers, if such are present, are in advance of all the 

 rest in their development as for instance in the peloric 

 Digitalis. In the red clover the main shoot consists of 

 a short upright rhizome, whereas the lateral branches 

 gradually increase in strength and develop into flowering- 

 stems. In Tctragonia cxpansa the main shoot is always 

 short and erect, terminating with a flower. The secon- 

 dary shoots often grow to more than a meter in length 

 and are much stronger. Instances of strengthening 

 shoots are the lateral branches which arise from the 

 axils of the radical leaves of many plants (Ranunculns 

 bulbosus), or from the middle part of the stem (Chry- 

 santlicnnim scgctuin and Trifolinni incarnatum) ; also 

 the forked inflorescences as in Saponaria officinalis. Re- 

 ]:>eating shoots are often runners, and then we have what 

 Braun calls ^'repetitional generations," as in Valeriana 

 officinalis, LysiniacJiia vulgaris, etc. 



See § 22,, p. 256. 



