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In a preliminary study of seasonal reproductive changes in stallions, four blood samples per week were collected on three separate days from each of four standardbred and two pony stallions for ten consecutive months. Each serum sample was analysed for testosterone, LH and FSH using radio-immunoassay techniques. During the same period paired ejaculates were collected one hour apart one day per week and volumes of both gel-free semen and gel, motility, spermatozoa/ml, total spermatozoa/ejaculate and pH were measured for each semen sample. Libido was monitored by recording reaction time and number of mounts/ejaculate for each collection. On the days of semen collection two blood samples were taken, one before sexual stimulation and one immediately after the first ejaculate. There was a marked effect of season on serum testosterone, LH and FSH levels, however the extent of change and timing of peak levels varies between stallions. Serum FSH levels started rising in late July-early August and generally reached a sharp peak during September, followed by a gradual decline thereafter. In several cases, testosterone showed a pattern of change similar to the of FSH, with peak levels occurring 2-4 weeks after FSH. This apparent association between these two hormones suggested that FSH may modify testosterone production possibly by altering the responsiveness to the testes to LH stimulation. In contrast, although LH levels began to rise at about the same time as FSH levels, peak values were not reached until November, two months after FSH peaked. The seasonal pattern of circulating LH levels more closely resembled the annual changes in daily photoperiod. These results, along with seasonal changes in seminal parameters, were consistent with the view that FSH is involved in initiating early seasonal changes in spermatogenic activity. There was some evidence for an inverse relationship between testicular function and FSH levels which supported the concept of a negative feedback on FSH secretion by a principle of testicular origin. Only LH was significantly (P

The present studies were carried out to investigate whether the leaves are concerned solely with hormone production or whether they are involved in the supply of photosynthates to lateral buds. Also as the earlier work on GA and IAA interaction present some conflicting results, it was decided to further investigate the interaction of these two hormones with special reference to the role of young leaves as a source of endogenous auxin.

It has been suggested that vegetative organs, i.e. the shoot apex, buds, stem tissue, and roots have some measure of control on apical dominance in Phaseolus vulgaris L. by contributing to the balance of hormones available for bud growth. The inhibitory influence, auxin, was produced by the shoot apex, leaves, to a lesser extent small lateral buds, and possibly also by the stem tissue. The shoot produced auxin interacted with cytokinin and gibberellin from the root system in the control mechanism. The root produced hormones were possibly acting to promote lateral growth. In the inhibited stage of lateral growth, the supply of root cytokinin, as studied by the use of ¹⁴C-kinetin was directed primarily to the apex and only small amounts of ¹⁴C -kinetin activity accumulated in the lateral buds. When the apex was removed significantly greater amounts of ¹⁴C -kinetin activity accumulated in the lateral buds. Only when the promotory factor became available to the buds, did significant outgrowth of lateral buds commence. The supply of hormones from their site of production in vegetative organs probably modifies the local hormone balance at the buds and regulates bud outgrowth.